A compound with molecular mass 180 is acetylated  to get a compound with molecular mass 390. The number of amino groups present per molecule of the former compound is

Increase in mwt after acetylation of one Amine is group = 42

$\begin{array}{l}\therefore 390-180=210\\ each acetyl group has a mass of 43 but \sin ce it replaces one hydrogen net weight added will be 42\\ \frac{210}{42}=5\end{array}$