When a mixture made up of sodium chloride and sodium hydrogencarbonate is heated, the reaction below occurs. $2\text{NaHCO}_3(s) \rightarrow \text{Na}_2\text{CO}_3(s) + \text{CO}_2(g) + \text{H}_2\text{O}(g)$. On heating, sodium chloride remains unchanged. If $6.0\,\text{g}$ of the mixture is heated, the mass decreases by $1.5\,\text{g}$. What percentage by mass of the mixture is sodium hydrogencarbonate? [$M_r$: $\text{NaHCO}_3$, $84$; $\text{Na}_2\text{CO}_3$, $106$; $\text{CO}_2$, $44$; $\text{H}_2\text{O}$, $18$]
- A$34\%$
- B$48\%$
- C$68\%$
- D$95\%$