Question

Write the SI unit of activity.
A. Becquerel
B. Henry
C. Ohm
D. Mendel

Answer 1

Hint: The activity of a radioactive sample has a dimensional unit of disintegrations per second or ${s^{ - 1}}$. The scientist Joseph Henry is famous for his contributions to electromagnetics and Gregor Mendel is the father of genetics.

Complete Step-by-Step answer
The activity of a radioactive sample is the number of disintegrations that happen every second. We know that atoms dissociate depending on the number of undissociated atoms present. The final expression for the number of Atoms present disintegrated $(N)$ and time elapsed $t$ is given as:
$N = {N_0}{e^{ - \lambda t}}$
Here ${N_0}$ is the number of atoms that we started with and $\lambda $ is the disintegration constant. A higher $\lambda $ signifies that disintegrations are happening faster.
We can see that the activity $R$ of the sample is:
$R = \dfrac{{dN}}{{dt}} = - {N_0}\lambda {e^{ - \lambda t}} = - \lambda N$ So activity and Disintegration constant $\lambda $ have the same unit of disintegrations per second.
The standard unit of Activity is Becquerel and represented by the symbol $Bq$. The activity of a sample is $1Bq$ if one disintegration happens in every 1 second.
Additional information:
There are other units of activity that were derived before Bq. Curie is another unit of activity, which is defined as the number of disintegrations per second that a Radium-226 sample undergoes.
$1{\text{Ci}} = 3.7 \times {10^{10}}Bq$
Another unit of activity is Rutherford, Rd. It is defined as ${10^6}Bq$. Thus, the activity is 1Rd if one million atoms disintegrate every second.

Note: Here, the options did not have Curie or Rutherford. But remember that the SI unit of activity is Becquerel $Bq$. Even if other units of activity were present, Bq would be the correct answer.