A certain radioactive isotope `._(Z)^(A)X(t_(1//2)=100` days decays to `._(Z-2)^(A-8)Y` . If 1 mole of `._(Z)^(A)X` is kept in sealed container , how much He gas will accumulate at STP in 200 days?
A. 11.2 litres
B. 33.6 litres
C. 22.4 litres
D. 44.8 litres