(a) Write two properties by which electric potential is related to the electric field .
(b) Two point charges `q_(1) and q_(2)` separated by a distance of `r_(12)` are kept in air. Derive an expression for the potential energy of the system of two charges .

Explanation

### Step-by-Step Solution

**(a) Two properties relating electric potential to electric field:**

1. **Electric Field as the Negative Gradient of Electric Potential:**
The electric field (E) is related to the electric potential (V) by the equation:
\[
E = -\frac{dV}{dr}
...