Which one of the following is an antibiotic?

Which of the following drugs is an analgesic?

$.........$ is a potent vasodilator.

The $-As=As-$ linkage is present in which of the following medicines?

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.

Which of the following statements is correct regarding the detergent $Sodium \ lauryl \ sulphate$?