Đáp án đúng: B
C2H6 ; C3H8
${{n}_{C{{O}_{2}}}}\,=\,{{n}_{CaC{{O}_{3}}\,\downarrow }}\,=\,0,25\,mol$
khối lượng nước vôi trong giảm 7,7 gam$\Rightarrow \,{{m}_{CaC{{O}_{3}}}}\,-\,{{m}_{C{{O}_{2}}}}\,-\,{{m}_{{{H}_{2}}O}}\,=\,7,7$
$\Rightarrow \,{{m}_{{{H}_{2}}O}}\,=\,6,3\,gam\,\Rightarrow \,{{n}_{{{H}_{2}}O}}\,=\,0,35\,mol\,>\,{{n}_{C{{O}_{2}}}}\,\Rightarrow \,ankan$
${{n}_{ankan}}\,=\,{{n}_{{{H}_{2}}O}}\,-\,{{n}_{C{{O}_{2}}}}\,=\,0,1\,mol$
Số C =$\frac{{{n}_{C{{O}_{2}}}}}{{{n}_{ankan}}}$ = 2,5 ⟹ C2H6; C3H8