How many methyl groups are present in $n-hexadecyl$ trimethyl ammonium chloride?

The $IUPAC$ names of the following compounds $A$ and $B$ are:

Urea upon hydrolysis yields

Nitrobenzene is prepared from benzene using a mixture of concentrated $HNO_3$ and concentrated $H_2SO_4$. In the nitrating mixture,$HNO_3$ acts as a ........

What is the $IUPAC$ name of isobutylamine?

What is the $IUPAC$ name of $CH_3CH_2NHCHO$?