Indicators MCQ Quiz - Objective Question with Answer for Indicators - Download Free PDF

Last updated on Jun 5, 2025

Latest Indicators MCQ Objective Questions

Indicators Question 1:

What is the approximate pH of a neutral salt solution?

  1. Depends on the temperature
  2. Less than 7 
  3. More than 7
  4. Equal to 7

Answer (Detailed Solution Below)

Option 4 : Equal to 7

Indicators Question 1 Detailed Solution

The correct answer is Equal to 7.

Key Points

  • A neutral salt solution has a pH of exactly 7 at standard temperature and pressure (25°C).
  • This occurs because the salt is formed from a strong acid and a strong base, which completely neutralize each other.
  • Examples of neutral salts include sodium chloride (NaCl) and potassium nitrate (KNO3).
  • The ions of neutral salts do not hydrolyze in water, maintaining a neutral pH in the solution.

Additional Information

  • pH Scale:
    • The pH scale ranges from 0 to 14, where 7 is neutral, < 7 is acidic, and > 7 is basic.
    • The pH is calculated as the negative logarithm of hydrogen ion concentration: pH = -log[H+].
  • Strong Acids and Bases:
    • Strong acids completely dissociate in water (e.g., HCl, HNO3).
    • Strong bases also dissociate completely (e.g., NaOH, KOH).
  • Hydrolysis of Salts:
    • Salts formed from strong acids and strong bases do not hydrolyze, resulting in a neutral solution.
    • However, salts formed from weak acids or bases may hydrolyze, affecting the pH.
  • Temperature Dependence:
    • The pH of pure water and neutral solutions is exactly 7 at 25°C.
    • As temperature increases, the pH of water decreases slightly due to increased ionization, but it remains neutral.

Indicators Question 2:

Which of the following statements is/are correct regarding the pH scale?

I. The pH of a neutral solution is 7.

II. Values more than 7 on the pH scale represent an acidic solution.

  1. Only I
  2. Only II 
  3. Both I and II
  4. Neither I nor II 

Answer (Detailed Solution Below)

Option 1 : Only I

Indicators Question 2 Detailed Solution

The correct answer is Option 1.

Key Points

  • The pH scale ranges from 0 to 14, where 7 is considered neutral.
  • The pH of a neutral solution, such as pure water, is exactly 7.
  • Values less than 7 on the pH scale represent an acidic solution.
  • Values greater than 7 on the pH scale represent a basic (alkaline) solution, not an acidic one.
  • The pH scale is logarithmic, meaning each whole number change represents a tenfold change in acidity/basicity.

Additional Information

  • Definition of pH
    • pH stands for 'potential of Hydrogen' or 'power of Hydrogen'.
    • It measures the hydrogen ion concentration in a solution.
  • Applications of pH Measurement
    • pH measurement is crucial in chemistry, biology, medicine, agriculture, and many other fields.
    • It is used to determine the acidity or alkalinity of soil, water, and other substances.
  • Indicators of pH
    • Litmus paper, pH paper, and pH meters are commonly used to measure pH.
    • Indicators change color at specific pH levels, providing a visual representation of pH.
  • Importance of pH in Biological Systems
    • Maintaining proper pH is essential for many biological processes.
    • Human blood has a pH of around 7.4, which is slightly basic.
    • Enzyme activity and metabolic functions are highly pH-dependent.

Indicators Question 3:

Which of the following will happen when an aqueous solution of ammonium chloride is tested with a litmus solution?

  1. It will turn blue litmus red.
  2. It will not affect the colour of litmus.
  3. It will turn blue litmus into a darker shade of blue.
  4. It will turn red litmus blue.

Answer (Detailed Solution Below)

Option 1 : It will turn blue litmus red.

Indicators Question 3 Detailed Solution

The correct answer is It will turn blue litmus red..

Key Points

  • Ammonium chloride (NH4Cl) is a salt that, when dissolved in water, undergoes hydrolysis to form a weak base (NH4OH) and a strong acid (HCl).
  • The solution of ammonium chloride is acidic in nature due to the presence of the strong acid (HCl).
  • When an acidic solution is tested with blue litmus paper, it turns red, indicating the presence of an acid.
  • This behavior confirms that the solution of ammonium chloride is acidic and will turn blue litmus paper red.

Additional Information

  • Hydrolysis of Salts
    • Hydrolysis refers to the reaction of a salt with water to form an acid and a base.
    • Salts derived from strong acids and weak bases produce acidic solutions.
    • Salts derived from strong bases and weak acids produce basic solutions.
  • Litmus Test
    • Litmus paper is a pH indicator used to test whether a solution is acidic or basic.
    • Blue litmus paper turns red under acidic conditions (pH < 7).
    • Red litmus paper turns blue under basic conditions (pH > 7).
  • Ammonium Chloride
    • Ammonium chloride is a white crystalline salt with the formula NH4Cl.
    • It is commonly used in fertilizers and as a flavoring agent in some types of licorice.
    • In a laboratory, it is used as a buffer solution and in the preparation of cooling baths.
  • pH Scale
    • The pH scale ranges from 0 to 14 and measures the acidity or basicity of a solution.
    • A pH of 7 is considered neutral.
    • pH values less than 7 indicate acidic conditions, while values greater than 7 indicate basic conditions.

Indicators Question 4:

Solid sodium bicarbonate was placed on a strip of pH paper. The colour of the strip:

  1. Turned blue
  2. Turned red 
  3. Turned green and slightly yellow
  4. Did not change

Answer (Detailed Solution Below)

Option 4 : Did not change

Indicators Question 4 Detailed Solution

The correct answer is Did not change.

Key Points

  • Sodium bicarbonate (NaHCO3) is a weak base and slightly alkaline in nature.
  • pH paper is an indicator that changes color based on the pH of the substance it comes into contact with.
  • Solid sodium bicarbonate typically has a pH around 8-9 when dissolved in water, but the solid form does not readily change the pH paper color.
  • The color of the pH paper does not change significantly because the bicarbonate ions in the solid form are not free to react with the paper.

Additional Information

  • pH Scale
    • The pH scale ranges from 0 to 14, where 7 is neutral, below 7 is acidic, and above 7 is basic (alkaline).
    • The pH paper is a tool used to measure the acidity or alkalinity of a solution.
  • Sodium Bicarbonate
    • Commonly known as baking soda, sodium bicarbonate is used in cooking, cleaning, and sometimes as a medicinal antacid.
    • It is a chemical compound with the formula NaHCO3.
  • Indicators
    • Indicators are substances that change color in response to changes in pH.
    • Common indicators include litmus paper, phenolphthalein, and methyl orange.
  • Reactivity of Solids
    • Solid compounds are generally less reactive with indicators compared to their aqueous solutions.
    • This is because the ions in solids are not free to interact with the indicator.

Indicators Question 5:

As the concentration of hydronium ions increases, the pH value _______. 

  1. decreases and then increases
  2. decreases 
  3. remains the same
  4. increases

Answer (Detailed Solution Below)

Option 2 : decreases 

Indicators Question 5 Detailed Solution

The correct answer is decreases.

Key Points

  • The pH value is a measure of the hydrogen ion concentration in a solution.
  • As the concentration of hydronium ions (H3O+) increases, the pH value decreases.
  • A lower pH value indicates a higher acidity of the solution.
  • The pH scale ranges from 0 to 14, with 7 being neutral, below 7 acidic, and above 7 basic.

Additional Information

  • Hydronium Ion (H3O+)
    • Hydronium ion is the form in which a proton (H+) exists in aqueous solution.
    • It is formed when an acid dissolves in water, donating a proton to a water molecule.
  • pH Scale
    • The pH scale is logarithmic, meaning each whole pH value below 7 is ten times more acidic than the next higher value.
    • For example, a solution with a pH of 3 is 10 times more acidic than a solution with a pH of 4.
  • Acidity and Alkalinity
    • Acidity refers to the concentration of hydrogen ions (H+) in a solution.
    • Alkalinity refers to the concentration of hydroxide ions (OH) in a solution.
  • Neutralization Reaction
    • A neutralization reaction occurs when an acid and a base react to form water and a salt.
    • This reaction generally results in the pH of the solution moving towards neutral (pH 7).

Top Indicators MCQ Objective Questions

Which of the following substance has a pH value of about 14?

  1. Blood 
  2. Sodium hydroxide
  3. Milk of magnesia
  4. Lemon Juice

Answer (Detailed Solution Below)

Option 2 : Sodium hydroxide

Indicators Question 6 Detailed Solution

Download Solution PDF

The correct answer is Sodium hydroxide.

Key Points 

  • Sodium hydroxide (NaOH) dissociates completely in water to give Na+ and OH−
  • Sodium hydroxide is considered a strong base as all the available [OH] in NaOH is present in the solution as [OH−] and available to accept protons.
  • Sodium hydroxide is the strongest base because it totally dissociates to form sodium ions and hydroxide ions.
  • These hydroxide ions are treated with hydrogen ions further from the acid and totally ionize the hydrogen ions.
  • Producers may utilize sodium hydroxide to manufacture soaps, rayon, paper, products that explode, dyes, and petroleum products.
  • Other works that may utilize sodium hydroxide comprise preparing cotton fabric, metal cleaning and preparing, oxide coating, electroplating, and electrolytic extraction.
  • It has the pH value of about 14.

Additional Information

  • The blood has a normal pH range of 7.35 to 7.45.
  • Milk of Magnesia is basic in nature. The pH value of the Milk of Magnesia is 10.5.
  • Lemon juice has a pH between 2 and 3.

pH of milk of magnesia is                  .

  1. 12
  2. 8
  3. 10
  4. 14

Answer (Detailed Solution Below)

Option 3 : 10

Indicators Question 7 Detailed Solution

Download Solution PDF

The correct answer is 10.

Key Points

  • Milk of Magnesia is the magnesium compound which acts as an antacid.
  • The term milk of magnesia was first used by English pharmacist Charles Henry Phillips in 1872.
  • Milk of Magnesia is basic in nature.
  • The pH value of the Milk of Magnesia is 10.

Additional Information

  • The scale used to express the acidic or alkaline nature of a substance based on the concentration of hydrogen ions in its solution is called a pH scale.
  • pH scale was discovered by Soren Sorensen.
    • The pH value of the acids are less than 7 (0 to 7)
  • Acid substances usually produce a sour taste.
    • The pH value of the Bases are greater than 7 (7 to 14)
  • Base substances usually produce a bitter taste.
  • The pH value of the neutral substance is equal to 7.
  • The pH value of the pure water is 7.
  • The pH value of the blood is close to 7.4.

Acid changes the colour of blue litmus to ________.

  1. yellow
  2. red
  3. pink
  4. orange

Answer (Detailed Solution Below)

Option 2 : red

Indicators Question 8 Detailed Solution

Download Solution PDF

The correct answer is Red.

Key Points

  •  Acid
    • Acid changes the colour of blue litmus to Red.
    • A Brnsted-Lowry acid or Lewis acid is a molecule or ion that can either donate a proton (the hydrogen ion, H+) or establish a covalent bond with an electron pair. Proton donors, also known as Brnsted-Lowry acids, are the first class of acids.
    • Proton donors, also referred to as Arrhenius acids, generate the hydronium ion H3O+ under the unique situation of aqueous solutions.
    • The Arrhenius theory was expanded upon by Brnsted and Lowry to take non-aqueous solvents into account.
    • A hydrogen atom is typically bound to a chemical structure in a Brnsted or Arrhenius acid that is still energetically advantageous after the loss of H+.

Additional Information

  • Aqueous Arrhenius acids have distinguishing characteristics that serve as a useful definition of an acid. Acids can turn blue litmus red, produce aqueous solutions with a sour taste, and react with bases and some metals (like calcium) to generate salts.
  • The Latin word acidus, which means "sour," is where the word acid comes from. While the technical definition solely refers to the solute, an aqueous solution of an acid with a pH lower than 7 is sometimes commonly referred to as "acid" (as in "dissolved in acid"..
  • Higher acidity and, thus, a higher concentration of positive hydrogen ions in the solution are indicative of a lower pH

Which of the following is natural acid-base indicator?

I. Litmus

II. Turmeric

  1. Only II
  2. Only I
  3. Neither I nor II
  4. Both I and II

Answer (Detailed Solution Below)

Option 4 : Both I and II

Indicators Question 9 Detailed Solution

Download Solution PDF

The correct answer is Both I and II.

Key Points

  • Indicators are the substances that are used to identify whether the given substance is an acid or a base.
  • There are two types of indicators:
    • Natural: These indicators are obtained from natural sources like plants. 
    • Turmeric, litmus, china rose petals, etc., are some of the naturally occurring indicators. Hence, option 4 is correct.
    • The most commonly used natural indicator is litmus.
    • It is extracted from lichens.
    • It is available in the form of a solution, or in the form of strips of paper, known as litmus paper.
    • Generally, it is available as red and blue litmus paper.
    • Man-made: Phenolphthalein, Methyl orange are some of the man-made indicators.

Important Points

  • The indicators change their color when added to a solution containing an acidic or a basic substance.
  • Turmeric is a natural indicator. It contains the substance curcumin which changes color with pH.
  • When a substance is basic, the color is red, whereas when the substance is acidic, the color of turmeric turns yellow to brown.
  • Films containing aqueous hibiscus extract were developed as a natural pH indicator.
  • Natural polymers (chitosan, gelatine, and starch) were used for the film production.
  • Great color changes from pink (pH = 2.0) to yellow (pH = 13.0) were observed.
  • Acids turn blue litmus red. Bases do not change the color of blue litmus.
  • Acids do not change the color of red litmus. Bases turn red litmus blue.

Additional Information 

Some indicators and their color change are given in the table below:

Indicator

Color Change in Acidic Solution

Color Change in Basic Solution

Phenolphthalein

Colorless

Pink

Methyl Orange

Red or Orange

Yellow

Litmus Paper

Red

Blue

Turmeric

Yellow

Red

Hibiscus Flowers  Pink  Yellow

China Rose

Dark pink

Green

The pH of a neutral solution is ______.

  1. 7
  2. 0
  3. 8
  4. 14

Answer (Detailed Solution Below)

Option 1 : 7

Indicators Question 10 Detailed Solution

Download Solution PDF

The correct answer is 7.

Key Points

  •  A solution's acidity can be determined by looking at its pH, which is a measurement of hydrogen ion concentration. Pure water slightly separates into ions with roughly equal amounts of hydrogen and hydroxyl (OH) ions. [H+] is 107 for a neutral solution, or pH = 7.
  • By chance, the amounts of H+ and OH- are equal at pH 7. Because of this, pH 7 is regarded as the neutral pH. The concentration of H+ exceeds the concentration of OH- below pH 7, causing the water to become acidic.
  • Because pure water has a pH of exactly 7, a pH value of 7 is considered neutral. Levels under 7 are considered acidic, whereas those over 7 are considered basic or alkaline.

Additional Information

  • pH stands for "Potential of Hydrogen" in its full form.
  • The negative logarithm of the concentration of H+ ions is known as pH.
  • As a result, the meaning of pH is defined as the strength or power of hydrogen.
  • For human life to exist, the serum's pH must be carefully regulated at around 7.4 (a slightly alkaline range of 7.35 to 7.45).

Who discovered pH scale?

  1. Lavoisier
  2. J.J Thompson
  3. Chadwick
  4. Sorensen

Answer (Detailed Solution Below)

Option 4 : Sorensen

Indicators Question 11 Detailed Solution

Download Solution PDF

The correct answer is Sorensen.

Key Points

  • The pH scale was invented by the Danish biochemist Soren Peter Lauritz Sorensen.
  • He introduced this scale in 1909 to measure the acidity and basicity of substances. 

Additional Information

pH Scale:

  • pH is a measure of how acidic/basic a substance is.
  • pH stands for the potential of hydrogen, which refers to the concentration of hydrogen ions in a solution.
  • The range goes from 0 - 14, with 7 being neutral. pHs of less than 7 indicate acidity, whereas a pH of greater than 7 indicates a base.
  • pH is really a measure of the relative amount of free hydrogen and hydroxyl ions in the water. 

What is the approximate pH of a neutral salt solution?

  1. Depends on the temperature
  2. Less than 7 
  3. More than 7
  4. Equal to 7

Answer (Detailed Solution Below)

Option 4 : Equal to 7

Indicators Question 12 Detailed Solution

Download Solution PDF

The correct answer is Equal to 7.

Key Points

  • A neutral salt solution has a pH of exactly 7 at standard temperature and pressure (25°C).
  • This occurs because the salt is formed from a strong acid and a strong base, which completely neutralize each other.
  • Examples of neutral salts include sodium chloride (NaCl) and potassium nitrate (KNO3).
  • The ions of neutral salts do not hydrolyze in water, maintaining a neutral pH in the solution.

Additional Information

  • pH Scale:
    • The pH scale ranges from 0 to 14, where 7 is neutral, < 7 is acidic, and > 7 is basic.
    • The pH is calculated as the negative logarithm of hydrogen ion concentration: pH = -log[H+].
  • Strong Acids and Bases:
    • Strong acids completely dissociate in water (e.g., HCl, HNO3).
    • Strong bases also dissociate completely (e.g., NaOH, KOH).
  • Hydrolysis of Salts:
    • Salts formed from strong acids and strong bases do not hydrolyze, resulting in a neutral solution.
    • However, salts formed from weak acids or bases may hydrolyze, affecting the pH.
  • Temperature Dependence:
    • The pH of pure water and neutral solutions is exactly 7 at 25°C.
    • As temperature increases, the pH of water decreases slightly due to increased ionization, but it remains neutral.

Which of the following statements is/are correct regarding the pH scale?

I. The pH of a neutral solution is 7.

II. Values more than 7 on the pH scale represent an acidic solution.

  1. Only I
  2. Only II 
  3. Both I and II
  4. Neither I nor II 

Answer (Detailed Solution Below)

Option 1 : Only I

Indicators Question 13 Detailed Solution

Download Solution PDF

The correct answer is Option 1.

Key Points

  • The pH scale ranges from 0 to 14, where 7 is considered neutral.
  • The pH of a neutral solution, such as pure water, is exactly 7.
  • Values less than 7 on the pH scale represent an acidic solution.
  • Values greater than 7 on the pH scale represent a basic (alkaline) solution, not an acidic one.
  • The pH scale is logarithmic, meaning each whole number change represents a tenfold change in acidity/basicity.

Additional Information

  • Definition of pH
    • pH stands for 'potential of Hydrogen' or 'power of Hydrogen'.
    • It measures the hydrogen ion concentration in a solution.
  • Applications of pH Measurement
    • pH measurement is crucial in chemistry, biology, medicine, agriculture, and many other fields.
    • It is used to determine the acidity or alkalinity of soil, water, and other substances.
  • Indicators of pH
    • Litmus paper, pH paper, and pH meters are commonly used to measure pH.
    • Indicators change color at specific pH levels, providing a visual representation of pH.
  • Importance of pH in Biological Systems
    • Maintaining proper pH is essential for many biological processes.
    • Human blood has a pH of around 7.4, which is slightly basic.
    • Enzyme activity and metabolic functions are highly pH-dependent.

Which of the following will happen when an aqueous solution of ammonium chloride is tested with a litmus solution?

  1. It will turn blue litmus red.
  2. It will not affect the colour of litmus.
  3. It will turn blue litmus into a darker shade of blue.
  4. It will turn red litmus blue.

Answer (Detailed Solution Below)

Option 1 : It will turn blue litmus red.

Indicators Question 14 Detailed Solution

Download Solution PDF

The correct answer is It will turn blue litmus red..

Key Points

  • Ammonium chloride (NH4Cl) is a salt that, when dissolved in water, undergoes hydrolysis to form a weak base (NH4OH) and a strong acid (HCl).
  • The solution of ammonium chloride is acidic in nature due to the presence of the strong acid (HCl).
  • When an acidic solution is tested with blue litmus paper, it turns red, indicating the presence of an acid.
  • This behavior confirms that the solution of ammonium chloride is acidic and will turn blue litmus paper red.

Additional Information

  • Hydrolysis of Salts
    • Hydrolysis refers to the reaction of a salt with water to form an acid and a base.
    • Salts derived from strong acids and weak bases produce acidic solutions.
    • Salts derived from strong bases and weak acids produce basic solutions.
  • Litmus Test
    • Litmus paper is a pH indicator used to test whether a solution is acidic or basic.
    • Blue litmus paper turns red under acidic conditions (pH < 7).
    • Red litmus paper turns blue under basic conditions (pH > 7).
  • Ammonium Chloride
    • Ammonium chloride is a white crystalline salt with the formula NH4Cl.
    • It is commonly used in fertilizers and as a flavoring agent in some types of licorice.
    • In a laboratory, it is used as a buffer solution and in the preparation of cooling baths.
  • pH Scale
    • The pH scale ranges from 0 to 14 and measures the acidity or basicity of a solution.
    • A pH of 7 is considered neutral.
    • pH values less than 7 indicate acidic conditions, while values greater than 7 indicate basic conditions.

Indicators Question 15:

Which of the following substance has a pH value of about 14?

  1. Blood 
  2. Sodium hydroxide
  3. Milk of magnesia
  4. Lemon Juice

Answer (Detailed Solution Below)

Option 2 : Sodium hydroxide

Indicators Question 15 Detailed Solution

The correct answer is Sodium hydroxide.

Key Points 

  • Sodium hydroxide (NaOH) dissociates completely in water to give Na+ and OH−
  • Sodium hydroxide is considered a strong base as all the available [OH] in NaOH is present in the solution as [OH−] and available to accept protons.
  • Sodium hydroxide is the strongest base because it totally dissociates to form sodium ions and hydroxide ions.
  • These hydroxide ions are treated with hydrogen ions further from the acid and totally ionize the hydrogen ions.
  • Producers may utilize sodium hydroxide to manufacture soaps, rayon, paper, products that explode, dyes, and petroleum products.
  • Other works that may utilize sodium hydroxide comprise preparing cotton fabric, metal cleaning and preparing, oxide coating, electroplating, and electrolytic extraction.
  • It has the pH value of about 14.

Additional Information

  • The blood has a normal pH range of 7.35 to 7.45.
  • Milk of Magnesia is basic in nature. The pH value of the Milk of Magnesia is 10.5.
  • Lemon juice has a pH between 2 and 3.
Get Free Access Now
Hot Links: teen patti cash game teen patti refer earn teen patti star login teen patti gold online teen patti master gold download