$X$ gồm $NaHSO_3, Na_2SO_3$ do phản ứng với $CaCl_2, Ca(OH)_2$
• P1:
$Na_2SO_3+CaCl_2\to CaSO_3+2NaCl$
$n_{CaSO_3}=\dfrac{c}{120}(mol)$
$\to n_{Na_2SO_3}=\dfrac{c}{120}(mol)$
• P2:
$NaHSO_3+Ca(OH)_2\to NaOH+CaSO_3+H_2O$
$n_{CaSO_3}=\dfrac{d}{120}(mol)$
$\to n_{NaHSO_3}=\dfrac{d}{120}(mol)$
$S+O_2\xrightarrow{{t^o}} SO_2$
$SO_2+2NaOH\to Na_2SO_3+H_2O$
$SO_2+NaOH\to NaHSO_3$
Ta có: $n_S=\dfrac{a}{32}(mol); n_{NaOH}=0,2b(mol)$
$\to \begin{cases} \dfrac{a}{32}=\dfrac{c}{120}+\dfrac{d}{120} \\ 0,2b=\dfrac{2c}{120}+\dfrac{d}{120}\end{cases}$
$\to \begin{cases} 3,75a=c+d\\ 24b=2c+d\end{cases}$
$\to d=3,75a-c=24b-2c$
$\to 3,75a-24b+c=0$