Assertion (A): Many fuel gases contain hydrogen as a major constituent.
Reason ( R): Liquid hydrogen is a very light fuel.

Options

A. Both (A) and ( R) are true and ( R) is the correct explanation for (A).
B. Both (A) and ( R) are true but (R ) is the correct explanation for (A).
C. (A) is true but ( R) is false.
D. (A) is false but (R ) is trues.

Explanation

To analyze the assertion and reason provided in the question, we will break it down step by step.

### Step 1: Understand the Assertion
The assertion states that "Many fuel gases contain hydrogen as a major constituent."

- **Analysis**: This is true. Hydrogen is indeed a significant component of many fuel gases, such as natural gas (which primarily consists of methane) and other hydrocarbon gases. Hydrogen is valued for its high calorific value, meaning it produces a large amount of energy when burned.

### Step 2: Understand the Reason
The reason states that "Liquid hydrogen is a very light fuel."

- **Analysis**: This statement is also true. Liquid hydrogen has a very low density compared to other fuels, making it a lightweight option. It is often used in applications such as rocket fuel due to its high energy content and low weight.

### Step 3: Evaluate the Relationship Between Assertion and Reason
Now, we need to determine if the reason correctly explains the assertion.

- **Analysis**: While both statements are true, the reason does not adequately explain why hydrogen is a major constituent in fuel gases. The assertion is supported more by the fact that hydrogen has a high calorific value, which makes it a desirable fuel, rather than its lightness.

### Conclusion
- **Final Evaluation**: The assertion is true, and the reason is true, but the reason is not the correct explanation for the assertion.

Thus, the correct answer would be:
- Assertion (A) is true.
- Reason (R) is true, but it does not explain (A).

### Answer:
The correct option is: Assertion is true, Reason is true, but Reason is not the correct explanation of Assertion.

---