Assertion : Number of atoms of He in 60 u of He is 15.
Reason : Atomic weight of He is 4 u.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion.
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion.
C. If Assertion is true statement but Reason is false.
D. If both Assertion and Reason are false statements.

Answer

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

### Step 1: Understand the Assertion
The assertion states that the number of atoms of Helium (He) in 60 u of He is 15.

### Step 2: Understand the Reason
The reason states that the atomic weight of He is 4 u. This is a known fact; the atomic weight of helium is indeed approximately 4 u.

### Step 3: Calculate the Number of Atoms
To determine if the assertion is correct, we can use the relationship between atomic weight and the number of atoms.

1. **Atomic weight of He** = 4 u means that 1 atom of He weighs 4 u.
2. To find the number of atoms in 60 u of He, we can use the formula:
\[ \text{Number of atoms} = \frac{\text{Total mass}}{\text{Mass of one atom}} \]
Substituting the values:
\[ \text{Number of atoms} = \frac{60 \, \text{u}}{4 \, \text{u/atom}} = 15 \, \text{atoms} \]

### Step 4: Conclusion
Since both the assertion and the reason are correct, we conclude that the assertion is true and the reason is true, and the reason correctly explains the assertion.

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