Which of the following is not a bactericidal antibiotic?

Arsenic-containing compounds are used in the treatment of ...... .

The given compound is used as:

Which of the following statements are correct?
$(i)$ Drugs that mimic natural messenger by switching on the receptor are called agonists.
$(ii)$ Shape of the receptor does not change after attachment of chemical messenger.
$(iii)$ $A$ cationic detergent is formed when stearic acid reacts with polyethylene glycol.
$(iv)$ Seldane is an antihistamine.

What is the use of sodium alkyl benzene sulfonate?

$4$-hydroxyacetanilide is commonly known as which of the following?