The correct option is A 72 %
The complete balanced equation is:
12Cl2+24KOH→21KCl+3KClO4+12H2O
12 moles of chlorine gives 3 moles of perchlorate.
2 moles of chlorine gives 0.5 moles of perchlorate.
Theoretical yield of perchlorate = 0.5 mole = 69.25 g
Experimental yield of perchlorate = 50 g
Percentage yield of perchlorate = experimental yieldtheoretical yield×100 = 50×10069.25=72%