X gồm: CH₄, C₂H₆O; C₃H₈O₃; C_nH_2nO₂

${{n}_{C{{H}_{4}}}}=2{{n}_{{{C}_{3}}{{H}_{8}}{{O}_{3}}}}$=> Qui về CH₄O; C₃H₈O

${{n}_{C{{O}_{2}}}}=0,31\,mol;\,{{n}_{{{O}_{2}}}}=0,305\,mol$

Coi hỗn hợp gồm: ${{C}_{m}}{{H}_{2m+2}}O:\,c\,mol;\,\,{{C}_{n}}{{H}_{2n}}{{O}_{2}}:b\,mol$

$\Rightarrow {{n}_{{{H}_{2}}O}}={{n}_{C{{O}_{2}}}}+{{n}_{ancol}}=0,31+c$

Bảo toàn O: ${{n}_{O\left( X \right)}}+2{{n}_{{{O}_{2}}}}=2{{n}_{C{{O}_{2}}}}+{{n}_{{{H}_{2}}O}}$

$\Rightarrow c+2b+0,305.2=0,31.2+0,31+c$

$\Rightarrow b=0,16\,mol$

$\Rightarrow {{n}_{X}}>0,16\,mol$

Số C trung bình $<{{n}_{C{{O}_{2}}}}/b=1,9375$

=> axit có 1 C (hỗn hợp ancol có ${{C}_{1}}:{{C}_{2}}:{{C}_{3}}$)

$\Rightarrow HCOOH,{{n}_{NaOH}}=0,2\,mol$

=> chất rắn gồm: 0,16 mol HCOONa; 0,14 mol NaOH dư

$\Rightarrow a=12,48g$

=> Đáp án C