Assertion: When a light wave travels from a rarer to a denser medium, it loses speed. The reduction in speed imply a reduction in energy carried by the light wave.
Reason: The energy of a wave is proportional to velocity of wave.

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 both assertion and reason are false.

Explanation

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

### Step 1: Analyze the Assertion
The assertion states that when a light wave travels from a rarer medium (like air) to a denser medium (like glass), it loses speed. This statement is true. According to the principles of optics, the speed of light decreases when it moves from a less dense medium to a more dense medium.

**Hint:** Remember that the speed of light is affected by the medium it travels through, and denser mediums slow down light.

### Step 2: Analyze the Reason
The reason states that the energy of a wave is proportional to the velocity of the wave. This statement is not correct. The energy carried by a wave is not directly proportional to its velocity; rather, it is more closely related to the amplitude of the wave. The frequency of the wave remains constant when transitioning between mediums, and thus the energy associated with the wave (which depends on amplitude and frequency) does not change.

**Hint:** Consider how energy in waves is defined and what parameters (like amplitude and frequency) influence it.

### Step 3: Conclusion
Since the assertion is true (light does lose speed when moving from a rarer to a denser medium), but the reason is false (energy is not proportional to velocity), we conclude that the assertion is true while the reason is false.

**Final Answer:** The assertion is true, but the reason is false.