$X:C_nH_mO_p$
$\begin{cases}44n_{CO_2}+18n_{H_2O}=b \\100n_{CaCO_3}=c\\b=0,71c \end{cases}\Rightarrow \begin{cases}n_{H_2O}=0,015c \\n_{CO_2}=0,01c \end{cases}$Mặt khác :
$c=\frac{a+b}{1,02}\Rightarrow a=1,02c-b=0,31c\Rightarrow n_O=\frac{a-2.0,015c-12.0,01c}{16}=0,01c$
$\Rightarrow n:m:p=0,01c:2.0,015c:0,01c=1:3:1\Rightarrow X:C_2H_6O_2$
$X:HO-CH_2-CH_2-OH$