The plant hormone used to destroy weeds in a field

Concept: 

• ‘Auxin’ is applied to the indole-3-acetic acid (IAA), and to other natural and synthetic compounds having certain growth regulating properties.
• It also helps to initiate rooting in stem cuttings.

Explanation:

• Synthetic auxins are used as weedicides.

Option 1:

• IBA (indole butyric acid ) is natural auxin.
• It plays a major role in inducing adventitious roots in stem cuttings. 
• Therefore, this is the incorrect option.

​Option 2:

• IAA (Indole acetic acid) is also natural auxin.
• It plays a major role in the elongation of plants and their development. 
• Therefore, this is the incorrect option.​

Option 3:

• NAA (Naphthalene acetic acid) is a synthetic auxin.
• It initiates the rooting process.
• It is also useful in plant tissue culture. 
• Therefore, this is the incorrect option.​

Option 4:

• 2, 4-D (2, 4-dichlorophenoxyacetic) is synthetic auxin. 
• 2,4-D is widely used to remove broad-leaved weeds or dicotyledonous weeds in cereal crops or monocotyledonous plants.
• It is also used to prepare weed-free lawns by gardeners. 
• Therefore, the correct answer is option 4.​​