It appears that one answer choice is missing. This question resembles one on my AP Chemistry practice test, where KCl would be the correct answer.
mass of AgCl = 2.23 - 0.80 = 1.43g AgCl
1.43g AgCl / 143g/mol AgCl = 0.01 moles AgCl
- The ratio of AgCl is 1:1, so:
moles of Ag+ = moles of Cl-, hence Ag+ has 0.01 moles and Cl- also has 0.01 moles
- MCl maintains the 1:1 ratio
moles of Cl- = moles of M+
- 0.01 moles of M+ and Cl-
0.01 Cl- = x/35.45 = 0.3545g Cl-
mass of MCl = 0.74g
0.74g MCl - 0.3545g Cl- = 0.3955g M+
0.3955g M+/x =0.010 mol M+
x= 39.55g M+
K+ has an approximate molar mass of 39.10
Thus, KCl is your answer
