Which of the following is the least basic?

Which of the following is the most basic compound?

Assertion : Acetamide reacts with $Br_2$ in presence of methanolic $CH_3ONa$ to form methyl $N$-methylcarbamate.
Reason : Methyl isocyanate is formed as an intermediate which reacts with methanol to form methyl $N$-methylcarbamate.

The most reactive amine towards dil. $HCl$ is . . . . . . .

Which of the following compounds reacts with aqueous nitrous acid at low temperature to give an oily substance,$N$-nitrosoamine?

The major product ($70\%$ to $80\%$) of the reaction between $m$-dinitrobenzene with $NH_4HS$ is