d
\((d)\) \((a)\) \(\mathop {M{e_2}NH}\limits_{{2^o}} > \mathop {MeN{H_2}}\limits_{{1^o}} > \mathop {M{e_3}N}\limits_{{3^o}} > N{H_3}\,\) if (\(R = -\) Meor Butyl) (in polar protic solvent)
\((b)\, 2^o > 3^o > 1^o > NH_3\) if \((R = -Et)\)
\((c)\, 3^o > 2^o > 1^o > NH_3\) (Gas phase)