Looks like you're missing an answer choice. I have this question on my practice test for AP Chemistry, the correct answer would be KCl.
mass AgCl = 2.23 - 0.80 = 1.43g AgCl
1.43g AgCl / 143g/mol AgCl = 0.01 moles AgCl
- AgCl has a mole ratio of 1:1 so:
moles Ag+ = moles Cl-, therefore Ag+ has 0.01 moles and Cl- has 0.01 moles
- MCl also has a 1:1 ration
moles Cl- = moles M+
- 0.01 moles of M+ and Cl-
0.01 Cl- = x/35.45 = 0.3545g Cl-
mass 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 a molar mass of approximately 39.10
Therefore KCl is your answer
