Assertion: Agricultural output increased several times after introduction of DDT.
Reason: DDT was the first insecticide used on a wide scale.

The correct answer is option 'D' - Both the assertion and the reason are true, but the reason is not a correct explanation of the assertion.

Explanation:

Assertion: Agricultural output increased several times after the introduction of DDT.

Reason: DDT was the first insecticide used on a wide scale.

Explanation:

DDT (Dichloro-Diphenyl-Trichloroethane) is an organochlorine insecticide that was widely used in the mid-20th century to control insect pests in agriculture. It was first synthesized in 1874, but its insecticidal properties were not discovered until 1939. DDT became popular due to its effectiveness in killing a wide range of insect pests and its low cost of production.

Agricultural output increased several times after the introduction of DDT:

1. DDT was highly effective in controlling agricultural pests, especially insects like mosquitoes, lice, and crop-damaging pests.
2. By eliminating or reducing the pest population, DDT helped protect crops from damage and increased agricultural productivity.
3. Increased agricultural output resulted in higher yields, leading to economic growth and improved food security.
4. DDT also played a crucial role in controlling vector-borne diseases like malaria, typhus, and dengue fever, which improved public health and reduced mortality rates.
5. The use of DDT in agriculture and public health programs contributed to the Green Revolution, a period of significant agricultural expansion and increased food production.

DDT was the first insecticide used on a wide scale:

1. DDT was the first synthetic insecticide to be widely used for agricultural and public health purposes.
2. Before the development of DDT, farmers relied on traditional methods like crop rotation, manual removal of pests, and the use of less effective insecticides.
3. DDT's introduction revolutionized pest control by providing a highly effective and affordable solution.
4. The success of DDT led to the development and use of other synthetic insecticides, further enhancing agricultural productivity.

Reason is not a correct explanation of the assertion:

While it is true that DDT was the first insecticide used on a wide scale, this fact alone does not directly explain the increase in agricultural output. The increase in agricultural output can be attributed to various factors, including improved farming practices, crop varieties, irrigation techniques, and mechanization, along with the use of effective insecticides like DDT.

Therefore, the assertion that agricultural output increased several times after the introduction of DDT is true, but the reason given is not a correct explanation for this increase.