Define the activity of a radio nuclide. Write its S.I. unit. Give a plot of the activity of a radioactive species versus time.
How long will a radioactive isotope, whose half life is T years, take for its activity to reduce to `1//8`th of its initial value ?

Explanation

### Step-by-Step Solution

1. **Define Activity of a Radio Nuclide:**
- The activity of a radioactive nuclide is defined as the rate at which the nuclide decays. Mathematically, it can be expressed as:
\[ A = -\frac{dN}{dt} \]
where \( A \) is the activity, \( N \) is the number of radioactive nuclei, and \( t \) is time.
...