Define Becquerel and Curie.

Becquerel: If a radioactive sample disintegrates at the rate of 1 disintegration per second, its activity (or decay rate R) is called 1 becquerel (Bq).
1 Bq = 1 disintegration/second. Bq is the SI unit of activity.
Curie (Ci): If a radioactive sample disintegrates at the rate of 3.7×10¹⁰ disintegration per second, its activity (or decay rate R) is called 1 curie (Ci).
$1\mathrm{Ci}=3.7\times {10}^{10}\mathrm{Bq}$