P - Block MCQ Quiz - Objective Question with Answer for P - Block - Download Free PDF

CONCEPT:

Dimerization of Nitrogen Oxides

• Some nitrogen oxides can undergo dimerization under specific conditions to form stable dimers.
• Dimerization usually occurs when the monomer has an unpaired electron or is a free radical. This allows the molecules to pair up and stabilize by forming a covalent bond or through other interactions.

EXPLANATION:

• NO₂ (Nitrogen dioxide): This molecule has an unpaired electron, making it a free radical. As a result, it can dimerize to form N₂O₄ (dinitrogen tetroxide) under suitable conditions, such as low temperatures.

Therefore, the nitrogen oxide that may dimerize is NO₂.

Reaction for dimerization of NO₂:

2NO₂ → N₂O₄

CONCEPT:

Behavior of Nitrogen, Arsenic, and Antimony in Compound Formation

• Elements like nitrogen, arsenic, and antimony belong to group 15 (pnictogens) of the periodic table and exhibit similar chemical properties due to their valence electron configuration.
• Nitrogen can form ammonia (NH₃) due to its ability to combine with hydrogen. Similarly, arsenic can form arsine (AsH₃), showcasing analogous behavior.
• Antimony (Sb), another group 15 element, can form antimony pentoxide (Sb₂O₅) under suitable conditions, as it exhibits oxidation states of +3 and +5.

EXPLANATION:

• Statement I: "Like nitrogen that can form ammonia, arsenic can form arsine."
  • This statement is correct because arsenic, like nitrogen, can react with hydrogen to form arsine (AsH₃). This is due to arsenic's chemical similarity to nitrogen as both belong to the same group in the periodic table.
• Statement II: "Antimony cannot form antimony pentoxide."
  • This statement is incorrect because antimony can form antimony pentoxide (Sb₂O₅) when it exhibits its +5 oxidation state. This is consistent with the behavior of group 15 elements.
• Therefore, Statement I is correct, but Statement II is incorrect.

Correct Answer: Option 3) Statement I is correct but Statement II is incorrect.

Correct Answer: C) A–1, B–2, C–6, D–4, E–5

Explanation:

CONCEPT:

Structure and Oxidation in Polythionates

• The general formula of a polythionate ion is S_n+1O₆²⁻.
• In such structures:
  • There are 2 terminal sulfur atoms, each bonded to 3 oxygen atoms (with oxidation state +5).
  • The remaining (n–1) sulfur atoms are unoxidized and exist in oxidation state 0.
• Total oxidation state contribution from all sulfur atoms = 2(+5) + (n–1)(0) = +10
• Average oxidation state of sulfur atoms = Total / (2 + n)
• The bond order of S–O bond is given as 5/3

EXPLANATION:

• 
  We are told that:

  Average oxidation state of S = Bond order of S–O = 5/3

• So:

  \(\frac{10}{2 + n} = \frac{5}{3}\)

• Cross-multiplying:

  \(10 \cdot 3 = 5 \cdot (2 + n)\\ \Rightarrow 30 = 10 + 5n \\ \Rightarrow 20 = 5n \\ \Rightarrow n = 4\)

Therefore, the value of n for the corresponding polythionate ion is: 4

Concept:

• Ionisation enthalpy:​

  • Ionisation enthalpy can be simply defined as the total amount of energy required to remove an electron from a gaseous atom in its isolated and gaseous state. The ionisation enthalpy can be distinguished in the order the electron is removed.

• Trend Of Ionisation Energy: In different sequential order, the trend changes: across the period and in a group.  

Explanation:

Across a Period:

• When progressing from left to right in a period, the factor that reduces is the element’s atomic radius. 
• As a result, as the size of an atom decreases, the attractive energy between the nucleus and the external electrons increases. Consequently, ionisation energy typically rises throughout a period in the periodic table.
• While in the second period in the periodic table, there exists a disparity in the tendency of ionisation enthalpy starting from boron to  beryllium. 
• Usually, the ionisation enthalpy of boron is higher when compared to the beryllium, but the same can’t be said for everything. The interpretation is that beryllium has full subshells, secondary to the penetration effect.
• Boron has 2s and 2p orbitals, whereas beryllium only has a 2s orbital. A 2s orbital has higher penetration energy than a 2p orbital.
• Therefore, the disposal of an electron through this 2p subshell becomes simpler when correlated to 2s the subshell in beryllium. 
• Consequently, due to these two aspects, the ionisation enthalpy of beryllium becomes higher when related to boron.

In a Group:

• As you move low in a group, the ionisation energy of the elements lessens, and the amount of orbit around the element goes up as you move down the group. The exterior orbital is where most electrons become distant from the nucleus. Also, the effective nuclear charge goes down. 

  Similarly, the shielding impact rises as you move towards the bottom of the group as the number of orbits rises which yields less ionisation energy.

• The elements in question are from Group 16 of the periodic table: Sulfur (S), Selenium (Se), Tellurium (Te), and Polonium (Po). As you move down the group, the ionization enthalpy generally decreases due to the increase in atomic size and the shielding effect.
• Sulfur (S)
• Selenium (Se)
• Tellurium (Te)
• Polonium (Po)

Therefore, the correct decreasing order is S > Se > Te > Po

Conclusion:

The correct option is  S > Se > Te > Po.

The correct answer is Nitric acid.

• Nitric acid is used in the purification of gold and silver.

Key Points

• Nitric acid is used in the purification of gold. The acid mixture aqua regia, or royal water, dissolves gold and is used to purify scrap alloy containing gold.
  • Aqua regia is a mixture of hydrochloric acid and nitric acid in a 3:1 ratio.
  • Nitric acid is a nitrogen oxoacid of formula HNO3 in which the nitrogen atom is bonded to a hydroxy group and by equivalent bonds to the remaining two oxygen atoms.

Important Points

The correct answer is Next to diamond, graphite is the second hardest known substance.

Key Points

• Allotropes of carbon:
  • Carbon allotropes refer to different well-defined structures of carbon-pure materials, in which carbon atoms are bonded in specific ways.
  • Carbon shows allotropic forms like Diamond, graphite, Fullerene.
    • Graphite:
      • Graphite is a good conductor of heat and electricity.
      • It is very soft and slippery and for this reason, graphite is used as a lubricant in the machine running at high temperatures, where oil cannot be used as a lubricant.
      • Every carbon atom in graphite is bonded to three other carbon atoms in such a way that a layered hexagonal structure is formed.
    • Diamond:
      • Diamond has a high density of 3.51 gm due to its three-dimensional giant structure.
      • It is a bad conductor of electricity.
      • Diamond is the hardest substance on earth.
      • It is used as an abrasive for sharpening hard tools.
    • Fullerenes are used as conductors.
      • It can be used as an absorber of gases.
      • Fullerenes are used as lubricants.
      • Some forms of fullerenes are used in making cosmetics-related ingredients.

Key Points

• Allotrope: The different structure of same chemical compound is called Allotrope.
• Buckminister fullerene is a stable structure of 60 carbon atoms.
• It is also known as Buckyball or just C60.
• The structure has 12 Pentagon rings and 20 hexagon rings.
• The structure is very strong and stable.

Additional Information

Other allotropes of Carbon are

• It is a hard, beautiful, crystalline allotrope of carbon.
• In an atom, each carbon atom is linked to four neighbouring carbon atoms.
• These have tetrahedral three-dimensional symmetry.
• Diamond doesn't have free electrons. So. it is a non-conductor of electricity.
• Diamond is a precious stone used in jewellery.

Graphite-

• It is a soft greyish black crystalline substance.
• It was discovered in 1795 by scientist 'Nicholas Jacques Conte'.
• Its's density is 1.9 to 2.3 g/cm3.
• Each carbon atom is attached to three other carbon atoms forming a 'Hexagonal planar structure'.
• Free electrons move through the layers of graphite, so graphite is a good conductor of electricity.

The correct answer is Diamond.

Key Points

• Diamond is the hardest substance on Earth.
• It has carbon atoms with four covalent bonds (four valence electrons is connected with four other carbon atoms).
• Diamond is the purest form of carbon.
• It is a non-metal that reflects light.
• It is a good insulator(bad conductor) of heat and electricity.
• It is used to drill rocks and to cut glasses.
• Diamond has a high density and high refractive index of 2.415.

Important Points

Allotropes

Substances with the same chemical properties but different physical properties are called allotropes.

Some of the allotropes of carbon are

• Diamond
• Graphite
• Buckminsterfullerene
• Charcoal

Additional Information

Buckminsterfullerene

It is a crystalline form of carbon.

• It was named after an American architect, Buckminster fuller.
• It consists of 60 carbon atoms joined to form a spherical molecule similar to a soccer ball. 
• The formula of 'Buckminsterfullerene' is C60.

Graphite

• It is chemically more reactive than diamond.
• It is a good conductor (bad insulator) of heat and electricity.
• Graphite has a hexagonal structure held by weak Vander Waal's force.

Uses:

• It is used as an electrode in furnaces.
• In a nuclear reactor, graphite is used as a moderator.
• It helps as a reducing agent in the steel manufacturing industry.

Iron

• Iron is the metal present in group 8 of the periodic table.
• Iron combined with nickel and chromium forms stainless steel.
• Wrought iron is known as the purest form of iron.
• In 2021, Karnataka became the largest producer of iron ore in India.​​

• In a diamond, the carbon atoms are arranged tetrahedrally.
• 98Each carbon atom is attached to four other carbon atoms 1.544 x 10-10 meters away with a C-C-C bond angle of 109.5 degrees.
• The structure is given as follows:

• It is a strong, rigid three-dimensional structure that results in an infinite network of atoms.

• This accounts for the diamond's hardness, extraordinary strength, and durability and gives the diamond a higher density than graphite (3.514 grams per cubic centimeter). Because of its tetrahedral structure, diamond also shows great resistance to compression.

The correct answer is Carbonic Acid.

• When carbon dioxide dissolves in water it gives Carbonic Acid.

Key Points

• When carbon dioxide dissolves in water it gives carbonic acid which can then become bicarbonate.
• This is how the carbonic acid shuttled around the body during aerobic respiration. 
• Carbonic acid, (H₂CO₃), a compound of the elements hydrogen, carbon, and oxygen.
  • It is formed in small amounts when its anhydride, carbon dioxide (CO₂), dissolves in water.
  • Carbonic acid plays a role in the assembly of caves and cave formations like stalactites and stalagmites.
  • Carbonic acid is widely used in the production of soft drinks, artificially carbonated sparkling wines, and other bubbly beverages.
  • Carbonic acid salts are called bicarbonates (or carbonates of hydrogen), and carbonates.

Additional Information

• Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2.
  • Usually encountered as a white solid, it is a weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms.
• Sulfuric acid or sulphuric acid, also known as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, and hydrogen, with the molecular formula H₂SO₄.
  • It is a colourless, odourless, and viscous liquid that is miscible with water.
• Acetic acid, systematically named ethanoic acid, is an acidic, colourless liquid and organic compound with the chemical formula CH₃COOH.
  • Vinegar is no less than 4% acetic acid by volume, making acetic acid the main component of vinegar apart from water.
  • Acetic acid is the second simplest carboxylic acid.

Key Points

• All the elements of the group 15 elements form tri oxides and pentoxides having the general formula M₂O₃ or M₂O₅.
• The oxides of Nitrogen, Phosphorus, and Arsenic are acidic.
• The trioxide of antimony Sb2O3 is amphoteric while that of bismuth Bi2O3 is basic.
• As2O3 is acidic in nature.
• The pentoxides of all these elements are acidic but acidic character decreases down the group.
• Thus, P₂O₅ is the strongest acidic oxide whereas Bi₂O₃  is the weakest acidic oxide.
• The acidic character of the same element increases with an increase in the oxidation state.

Hence, the most acidic oxide among the following is P2O5.

​Important Points

Facts about P₂O₅:

•  It is also written as P₄O₁₀ and is called phosphorus pentoxide.
• It is prepared by burning phosphorus in excess of air or oxygen. It is a white solid which sublimes on heating.
• It is a strong dehydrating agent and dehydrates nitric acid as well as sulphuric acid.
• The structure is:

​

Additional Information

• N₂O₅ is the most acidic of group 15 elements. 

The correct answer is CO + N₂

• Producer gas is a mixture of CO + N₂

Key Points

• Producer gas:
  • A typical producer gas obtained from coke contains 27% carbon monoxide, 12% hydrogen, 0.5% methane, 5% carbon dioxide and 55% nitrogen, by volume.
  • Producer gas is fuel gas that is made from material such as coal.
  • A combustible mixture of nitrogen, carbon monoxide, and hydrogen gives the producer gas. 
  • It is the cheapest gaseous fuel; however, its calorific value is not very high because it has a large proportion of nitrogen.
  • It is made by the partial combustion of carbonaceous substances usually coal, in an atmosphere of air and steam. 

Additional Information

• Coal gas is a mixture of H₂, CH₄, CO, and gases like N₂, C₂, H₄, O₂, etc. 
• Oil gas is a mixture of H₂, CH₄, C₂H₄, CO, and other gases like CO₂.
• Syngas, or synthesis gas, is a fuel gas mixture consisting primarily of hydrogen, carbon monoxide, and very often some carbon dioxide. 

The correct answer is Sea.

Key Points

• Out of the options, the greatest source of halogens is Sea.
  • Halogens are a group of elements in the periodic table that include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
  • These elements are very reactive and don't often occur in their pure form in nature.
  • Instead, they are commonly found combined with other elements, predominantly as salts dissolved in seawater.
  • Seawater: Contains large amounts of dissolved salts, including sodium chloride (NaCl), magnesium chloride (MgCl₂), and potassium chloride (KCl).
    • These salts release chloride (Cl) and, to a lesser extent, bromide (Br) and iodine (I) when dissolved in water.

Additional Information

• Lake water: While it also contains dissolved salts, the concentration of halogens in lakes is generally much lower than in seawater.
• Emissions from automobiles: Although car exhaust might contain trace amounts of certain halogens like chlorine from combustion or brake pads, it's not a significant source compared to the vast reservoirs in seawater.
• Facts about halogens:
  • They play crucial roles in various biological processes, like thyroid function in humans.
  • Some halogens have industrial applications, like chlorine in disinfecting water and bromine in flame retardants.
  • Due to their high reactivity, halogens can also be harmful if not handled properly.

Concept:

Carbon-carbon bond length is maximum in diamond because the diamond has a purely single bond.

The carbon atoms are held by strong covalent bonds and are arranged in a three-dimensional tetrahedral structure. Due to which diamond is hard. All the C-C bond are of the same length is 1.54 nm. In this rigid network, none of the carbon atoms can move. This accounts for the fact that diamonds are so hard and have such a high melting point.

While graphite, C₇₀ (fullerene), and C₆₀ (Buckminsterfullerene) single and partial double bonds.