a,
$n_{HCl}=0,2(mol)=n_X$
$\Rightarrow$ X có 1 nhóm amino
$n_{NaOH}=0,5.0,4=0,2(mol)=n_X$
$\Rightarrow$ X có 1 nhóm cacboxylic
CTTQ X: $NH_2RCOOH$
$NH_2RCOOH+HCl\to ClNH_3RCOOH$
$NH_2RCOOH+NaOH\to NH_2RCOONa+H_2O$
$n_{ClNH_3RCOOH}=n_{HCl}=0,2(mol)$
$\Rightarrow M=\dfrac{25,1}{0,2}=125,5$
$\Rightarrow M_R=125,5-45-17-35,5=28 (C_2H_4)$
Vậy CTPT X là $C_3H_7O_2N$
b,
CTCT:
$NH_2-CH_2-CH_2-COOH$
$CH_3-CH(NH_2)-COOH$