Which one of the following is the unit of activity of a radioactive source?

The unit of activity of a radioactive source is the Becquerel (Bq). Radioactivity refers to the frequency of radioactive decay or disintegrations per unit time produced by a given amount of material [t1]. One becquerel is defined as one radioactive decay or disintegration per second [t1][t4][t5]. It is the International System of Units (SI) derived unit for radioactivity, named after Henri Becquerel, the discoverer of radioactivity [t3][t5][t7]. Other options are incorrect as Lux is the unit of illuminance [t7], Tesla is the unit of magnetic flux density [t7], and Siemens is the unit of electrical conductance [t7]. While the Curie (Ci) is also a common unit for measuring radioactivity, particularly in the U.S., the Becquerel remains the standard SI unit for expressing the strength of a radioactive source [t1][t2][t6].

Sources

1. [1] https://www.epa.gov/radiation/radiation-terms-and-units
2. [2] https://remm.hhs.gov/radmeasurement.htm