Assertion: In an AC, only capacitor circuit has instaneous power equal to zero at any instant of time.
Reason: Phase difference current function and voltage function is `90^(@)`.

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 the correct explanation of Assertion.
C. If Assertion is true but Reason is false.
D. If Assertion is false but Reason is true.

Explanation

To solve the given assertion and reason question, we need to analyze both the assertion and the reason step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion:**
- The assertion states that in an AC circuit, only a capacitor circuit has instantaneous power equal to zero at any instant of time.
- This implies that for a purely capacitive circuit, the power does not change with time and remains zero.

2. **Understanding the Reason:**
- The reason provided states that the phase difference between the current function and the voltage function in a capacitor circuit is 90 degrees.
- In a purely capacitive circuit, the current leads the voltage by 90 degrees.

3. **Analyzing the Power in a Capacitive Circuit:**
- The instantaneous power \( P(t) \) in an AC circuit is given by the formula:
\[ P(t) = V(t) \cdot I(t) \]
- For a capacitor, the voltage \( V(t) \) can be expressed as:
\[ V(t) = V_0 \sin(\omega t) \]
- The current \( I(t) \) will lead the voltage by 90 degrees, so it can be expressed as:
\[ I(t) = I_0 \sin\left(\omega t + \frac{\pi}{2}\right) = I_0 \cos(\omega t) \]

4. **Calculating Instantaneous Power:**
- Now substituting \( V(t) \) and \( I(t) \) into the power formula:
\[ P(t) = V_0 \sin(\omega t) \cdot I_0 \cos(\omega t) \]
- Using the identity \( \sin(\theta) \cos(\theta) = \frac{1}{2} \sin(2\theta) \):
\[ P(t) = \frac{1}{2} V_0 I_0 \sin(2\omega t) \]
- This shows that the instantaneous power is not zero; it varies with time.

5. **Conclusion:**
- The assertion that instantaneous power is equal to zero at any instant of time in a purely capacitive circuit is **false**.
- The reason that the phase difference between current and voltage is 90 degrees is **true**.
- Therefore, the correct conclusion is that the assertion is false, and the reason is true.

### Final Answer:
- Assertion: False
- Reason: True