How can aniline be purified?

In the following reactions,$P$,$Q$,$R$,and $S$ are the major products.
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The correct statement about $P$,$Q$,$R$,and $S$ is

The major product in the following reaction is:

Which of the following does not react with $HNO_2$?

Which of the following reactions of a diazonium salt involves the retention of the diazonium group?

Carbylamine is liberated when $.....$ is heated with chloroform and alcoholic potash.