JEE Main 2019 Physics question

A sample of radioactive material A, that has an activity of 10 mCi (1 Ci = decays/s), has twice the number of nuclei as another sample of different radioactive material B which has an activity of 20 mCi. The correct choices for half-lives of A and B would then be respectively:

• (A)10 days and 40 days
• (B)20 days and 10 days
• (C)5 days and 10 days
• (D)20 days and 5 daysCorrect