200 g of a sample of KI is dissolved in 20 mL of 1.2 M KMnO₄ solution in acidic medium. After complete reaction, the solution is diluted to 150 mL, 25 mL of this diluted solution requires 40 mL of 0.5 M K₂Cr₂O₇ solution for complete reaction with the remaining KI. The percentage purity of KI sample is (K=39; I=127)
A) 60
B) 70
C) 80
D) 90