Which of the following is effectively used instead of DDT?

BHC (Benzene Hexachloride), also known as Lindane, is an organochlorine insecticide that serves as an effective alternative to DDT. While BHC shares similar environmental concerns due to its persistence, it belongs to the same chemical class and was widely adopted for pest control purposes.

The other compounds lack insecticidal properties: $\mathrm{CHCl}_3$ is a solvent and anesthetic, $\mathrm{CH}_2\mathrm{Cl}_2$ is a solvent, and picric acid functions as an explosive and antiseptic.

The correct alternative is therefore $\boxed{A}$.