A Capacitor blocks d.c. and allows a.c. Why ?

Explanation

### Step-by-Step Solution:

1. **Understanding Capacitors**: A capacitor is a two-terminal electronic component that stores electrical energy in an electric field. It consists of two conductive plates separated by an insulating material (dielectric).

2. **Behavior with Direct Current (DC)**: When a DC voltage is applied across a capacitor, the capacitor charges up to the voltage level of the source. Once fully charged, the current stops flowing because the capacitor acts like an open circuit. The frequency of a DC source is 0 Hz.

3. **Capacitive Reactance (Xc)**: The opposition that a capacitor offers to alternating current (AC) is called capacitive reactance, denoted as Xc. The formula for capacitive reactance is:
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