A parent nucleus X is decaying into daughter nucleus Y which in turn decays to Z. The half lives of X and Y are 40000 years and 20 years respectively. In a certain sample, it is found that the number of Y nuclei hardly changes with time. If the number of X nuclei in the sample is `4 xx 10^(20)`, the number of Y nuclei present in its is–

Options

A. `2 xx 10^(17)`
B. `2 xx 10^(20)`
C. `4 xx 10^(23)`
D. `4 xx 10^(20)`

Answer

A