Option 1: DDT is a pesticide that was widely used in the past for controlling mosquitoes and agricultural pests. However, it is not commonly used by farmers to destroy weeds. DDT has been banned in many countries due to its harmful effects on the environment and human health.

Option 2: Malathion is an insecticide that is used to control insects, such as mosquitoes and fruit flies. It is not commonly used by farmers to destroy weeds.

Option 3: Methyl bromide is a fumigant used to control pests in stored products and farm soils. While it is used in agriculture, it is primarily used to control pests, not weeds.

Option 4: 2,4-D (2,4-dichlorophenoxyacetic acid) is a commonly used herbicide that farmers use to destroy weeds. It is a selective herbicide, meaning it kills certain types of plants without harming the desired crops. It is commonly used to control broadleaf weeds in crops such as corn, soybeans, and wheat. 2,4-D is effective in controlling many types of weeds and is widely used in agricultural practices.

In summary, the correct option is 4) 2,4-D, as it is commonly used by farmers