Assertion : The number of electrons ejected from a metal surface depend upon the frequency of light.
Reason : There is a time lag between the striking of light beam and the ejection of electrons from the metal surface.

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 analyze the given assertion and reason, we will break down the statements and evaluate their correctness step by step.

### Step 1: Understand the Assertion
The assertion states: "The number of electrons ejected from a metal surface depends upon the frequency of light."

- **Explanation**: According to the photoelectric effect, electrons are ejected from a metal surface when light of sufficient frequency (greater than the threshold frequency) strikes it. The number of electrons ejected does indeed depend on the frequency of the incident light. If the frequency is below the threshold frequency, no electrons will be emitted, regardless of the intensity of the light. However, if the frequency is above the threshold frequency, the number of electrons emitted can also depend on the intensity of the light.

### Step 2: Evaluate the Assertion
- **Conclusion**: The assertion is partially correct because while the frequency is a crucial factor, it does not solely determine the number of electrons ejected. Therefore, the assertion is **not entirely true**.

### Step 3: Understand the Reason
The reason states: "There is a time lag between the striking of light beam and the ejection of electrons from the metal surface."

- **Explanation**: In the context of the photoelectric effect, there is no time lag between the light striking the metal surface and the ejection of electrons. When light of sufficient frequency hits the metal, electrons are emitted almost instantaneously.

### Step 4: Evaluate the Reason
- **Conclusion**: The reason is **incorrect** because it misrepresents the behavior of electrons in the photoelectric effect.

### Step 5: Final Conclusion
Both the assertion and the reason are incorrect. Thus, the correct answer to the question is that both the assertion and reason are false.

### Final Answer
Both the assertion and reason are false.

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