$n_X=0,1.0,3=0,03(mol)$
$n_{NaOH}=0,048.1,25=0,06(mol)$
$\dfrac{n_{NaOH}}{n_X}=2$
$\Rightarrow X$ có 2 nhóm $COOH$
Muối: $(NH_2)_xR(COONa)_2$
Bảo toàn Na: $n_{\text{muối}}=0,03(mol)$
$\Rightarrow M=\dfrac{5,31}{0,03}=177=16x+R+(44+23).2$
$\Leftrightarrow R=43-16x$
$x=1\Rightarrow R=27(C_2H_3)$
Vậy X là $CH_3-C(NH_2)(COOH)_2$ hoặc $HOOC-CH(NH_2)-CH_2-COOH$