The group of chemicals used as pesticide is

We need to identify which group of chemicals are all used as pesticides. Pesticides is a broad term that includes insecticides (kill insects), herbicides (kill weeds), fungicides (kill fungi), and rodenticides (kill rodents).

Analyzing each chemical mentioned in the options:

Aldrin: Aldrin is a chlorinated hydrocarbon compound that was widely used as an insecticide, particularly for soil-dwelling pests. It is a pesticide. (Present in Options 1 and 2)

Sodium Chlorate ($$NaClO_3$$): Sodium chlorate is a powerful oxidizing agent that is used as a non-selective herbicide (weed killer). It kills plants by disrupting their cellular processes. It is a pesticide. (Present in Options 1 and 3)

Sodium Arsenite ($$Na_3AsO_3$$ or $$NaAsO_2$$): Sodium arsenite is a highly toxic arsenic compound used as a pesticide (insecticide and herbicide). It has been used to control various pests and weeds. It is a pesticide. (Present in Options 1 and 4)

DDT (Dichlorodiphenyltrichloroethane): DDT is a well-known chlorinated insecticide. It is a pesticide. (Present in Options 2 and 3)

PAN (Peroxyacetyl nitrate): PAN is a secondary air pollutant formed in photochemical smog. It is NOT a pesticide - it is an atmospheric pollutant. (Present in Option 3)

Dieldrin: Dieldrin is a chlorinated hydrocarbon insecticide, related to aldrin (aldrin converts to dieldrin in the environment). It is a pesticide. (Present in Option 4)

Tetrachloroethene ($$C_2Cl_4$$): Tetrachloroethene (also called perchloroethylene or PCE) is primarily used as a dry cleaning solvent and degreasing agent. It is NOT classified as a pesticide. (Present in Option 4)

Evaluating the options:

Option 1: Aldrin (pesticide), Sodium Chlorate (pesticide), Sodium Arsenite (pesticide) - ALL are pesticides.

Option 2: DDT (pesticide), Aldrin (pesticide) - both are pesticides, but this is an incomplete group (only two).

Option 3: Sodium chlorate (pesticide), DDT (pesticide), PAN (NOT a pesticide) - incorrect.

Option 4: Dieldrin (pesticide), Sodium arsenite (pesticide), Tetrachloroethene (NOT a pesticide) - incorrect.

The correct answer is Option 1: Aldrin, Sodium Chlorate, Sodium Arsenite. All three are pesticides used for different purposes (insecticide, herbicide, and general pesticide respectively).