Answer : 2. "Allethrins "
Explanation :

(B) Allethrins

Allethrins are active chemicals commonly used in mosquito repellents and insecticides to deter or eliminate mosquitoes. They belong to a class of synthetic pyrethroid insecticides, which are designed to mimic the insecticidal properties of pyrethrins, natural insecticides derived from chrysanthemum flowers. These chemicals are effective in repelling and killing mosquitoes and other insects. The other options (Benzene Hexachlorophene, Atropine, and 2-Isopropoxiphimyal) are not typically used for mosquito control.