83.23 %
We are given;
We are required to get the mass percent of NH₄Cl in the original sample
Mass of NH₄Cl = Total mass of the mixture - remaining mass after sublimation
= 12.94 g - 2.17 g
= 10.77 g
% of NH₄Cl by mass =(Mass of NH₄Cl÷Total mass of original sample)×100
= (10.77 g ÷ 12.94 g) × 100
= 83.23 %
Therefore, the percent by mass of NH₄Cl in the original sample is 83.23%