Question

Which of the following is/are organic herbicide(s) ?
A. 2, 4-D
B. 2, 4, 5-T
C. Atrazine
D. Sodium arsenite
Choose the correct answer from the options given below:

• A. A, B and D only
• B. B, C and D only
• C. A, B and C only
• D. D only

Hint:

If a herbicide contains metal ions or mineral acids (like sodium, arsenic, copper, chlorates, or borates) without carbon complexes, it is inorganic. Chlorinated hydrocarbons and heterocyclic rings (like phenoxy compounds and triazines) are always organic.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Herbicides are chemical compounds used to destroy or inhibit the growth of unwanted plants and weeds.
They can be broadly classified based on their chemical composition into organic herbicides (containing carbon-hydrogen structures) and inorganic herbicides (lacking carbon, often composed of inorganic salts or metals).

Step 2: Detailed Explanation:
Let us analyze the chemical nature of each listed herbicide:
1. 2,4-D (A):
2,4-Dichlorophenoxyacetic acid is an organic chemical compound belonging to the phenoxy family of herbicides.
It mimics the plant hormone auxin, causing rapid, uncontrolled growth in broadleaf weeds, which leads to vascular collapse and death.
Since it is a carbon-based synthetic organic molecule, it is an organic herbicide.
2. 2,4,5-T (B):
2,4,5-Trichlorophenoxyacetic acid is another synthetic organic herbicide in the phenoxy family.
Historically, a $1:1$ mixture of 2,4-D and 2,4,5-T formed "Agent Orange."
It is also a carbon-based synthetic organic molecule.
3. Atrazine (C):
Atrazine is a synthetic organic compound of the triazine class.
It is used to prevent pre- and post-emergence broadleaf weeds by inhibiting photosynthesis.
Since it is an organic ring compound containing carbon and nitrogen, it is an organic herbicide.
4. Sodium arsenite (D):
Sodium arsenite ($\text{NaAsO}_2$) is an inorganic salt of arsenic.
Historically, it was used as a non-selective herbicide, soil sterilant, and sheep dip.
Because its chemical structure is an inorganic metallic salt and does not contain carbon-hydrogen bonds, it is classified as an inorganic herbicide.
Therefore, the organic herbicides in this list are A, B, and C.

Step 3: Final Answer:
2,4-D, 2,4,5-T, and Atrazine are organic herbicides, whereas sodium arsenite is an inorganic herbicide.
Therefore, the correct option is (C).