What is obtained upon the reduction of a Schiff base?

The basic character of ethylamine,diethylamine,and triethylamine in chlorobenzene is:

How can aniline be purified?

Given below are two statements:
Statement $I$: Primary aliphatic amines react with $HNO_2$ to give unstable diazonium salts.
Statement $II$: Primary aromatic amines react with $HNO_2$ to form diazonium salts which are stable even above $300 \ K$.
In the light of the above statements,choose the most appropriate answer from the options given below:

$R + CH_3-CO-CH_3 \xrightarrow{H^{+}} \text{Schiff's base}$. What is $R$ in this reaction?

In sets $A - D$, only one of the sets is incorrect regarding basic strength. Select it.