What are the drugs that bind to the receptor site and inhibit its natural function called?

In the given reaction scheme,$P$ is a phenyl alkyl ether,$Q$ is an aromatic compound; $R$ and $S$ are the major products.
$P$ $\xrightarrow{HI} Q$ $\xrightarrow[\text{(iii) } H_3O^{+}]{\text{(i) } CO_2, \text{(ii) } NaOH} R$ $\xrightarrow[\text{(ii) } H_3O^{+}]{\text{(i) } (CH_3CO)_2O} S$
The correct statement about $S$ is:

Veronal,a barbiturate drug,is used as:

Among the following,the number of tranquilizer/s is/are $.......$.
$A.$ Chlordiazepoxide
$B.$ Veronal
$C.$ Valium
$D.$ Salvarsan

What is tincture of iodine? What is its use?

An artificial sweetener $X$ is a halogen-containing compound and artificial sweetener $Y$ is a sulphur-containing compound. $X$ and $Y$ respectively are: