Assertion : Spherical shell a in the shown figure has a charge `-q` and shell B has charge `+q`. When these two are connected by a thin conducting wire, then whole of the electrostatic potential energy stored between the shell is lost.
Reason : Whole of the inner charge will transfer to outer shell B.

Options

A. If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
B. If both Assertion and Reason are true but Reason is not correct explanation of Assertion.
C. If Assertion is true but Reason is false.
D. If Assertion is false but Reason is true.

Answer

To solve the question, we need to analyze the assertion and reason provided regarding the electrostatic potential energy between two charged spherical shells when they are connected by a conducting wire.

### Step-by-Step Solution:

1. **Understanding the Charges on the Spherical Shells**:
- Shell A has a charge of \(-q\).
- Shell B has a charge of \(+q\).

2. **Connecting the Shells**:
- When the two shells are connected by a thin conducting wire, charge can flow between them until they reach the same potential.

3. **Electrostatic Potential Energy**:
- The electrostatic potential energy \(U\) between two point charges (or spherical shells) can be expressed as:
\[ U = \frac{1}{4\pi \epsilon_0} \frac{q_1 q_2}{R} \]
- Here, \(q_1 = -q\) and \(q_2 = +q\), and \(R\) is the distance between the centers of the two shells.

4. **Calculating Initial Potential Energy**:
- Substituting the values into the formula:
\[ U = \frac{1}{4\pi \epsilon_0} \frac{(-q)(+q)}{R} = -\frac{q^2}{4\pi \epsilon_0 R} \]
- The negative sign indicates that the energy is attractive.

5. **Charge Neutralization**:
- When the shells are connected, the negative charge from shell A will neutralize the positive charge on shell B.
- The total charge after connection will be:
\[ -q + q = 0 \]

6. **Final Potential Energy**:
- With a total charge of 0, the potential energy \(U\) between the shells becomes:
\[ U = 0 \]
- Therefore, all the initial electrostatic potential energy is lost.

7. **Conclusion**:
- The assertion states that the whole of the electrostatic potential energy stored between the shells is lost, which is correct.
- The reason states that the whole of the inner charge will transfer to the outer shell B, which is also correct as the charges neutralize each other.

### Final Answer:
Both the assertion and reason are correct, and the reason correctly explains the assertion.