Step 1: Understanding the Question:
This question tests knowledge of herbicide formulations.
Step 2: Detailed Explanation:
2,4-D is commonly formulated as an amine-salt (C).
It is also available as ester formulations, but amine-salts are more common for post-emergence application.
Ethyl ester (A): A formulation of 2,4-D.
Na-salt (B): Also a formulation.
Isopropyl amine (D): Also a formulation.
But the most common formulation is amine-salt.
Thus, the correct answer is amine-salt.
Step 3: Final Answer:
Thus, 2,4-D is formulated as amine-salt, which corresponds to option (C).
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