A sample containing sodium hydrogencarbonate mixed with sodium chloride is heated. The reaction equation for the decomposition of sodium hydrogencarbonate on heating is shown. $\mathrm{2NaHCO_3(s) \rightarrow Na_2CO_3(s) + CO_2(g) + H_2O(g)}$. Sodium chloride does not change when heated. If $6.0\,\mathrm{g}$ of the mixture is heated and the decrease in mass is $1.5\,\mathrm{g}$, what is the percentage by mass of sodium hydrogencarbonate in the mixture? [relative molecular mass, $M_r$: $\mathrm{NaHCO_3}$, 84; $\mathrm{Na_2CO_3}$, 106; $\mathrm{CO_2}$, 44; $\mathrm{H_2O}$, 18]
- A34%
- B48%
- C68%
- D95%