SOLUTION :
Sodium nitrate on heating is converted to sodium nitrite and oxygen gas is lost during decomposition.
$\begin{array}{l}2 NaNO _{3}=2 NaNO _{2}+ O _{2} \\2(23+14+48) \\=170 g\end{array}$
$\because \quad$ Loss of $32 g O _{2}$ when $170 g NaNO 3$ heated
$\therefore \quad 0.853 g O _{2}$ lost when $\frac{170 \times 0.853}{32} g NaNO _{3}$ heated
Total weight of $NaNO _{3}$ taken $=8.53 g$
Hence, the percentage of $NaNO _{3}$ which has decomposed
$=\frac{170 \times 0.853}{32} \times \frac{100}{8.53}= 5 3 \cdot 1 2 5 \% \text {. }$
