A: `1 "a.m.u." = 1.66 xx 10^(-24)` gram.
R: Actual mass of one atom of C-12 is equal to `1.99 xx 10^(-23) g`

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 problem, we need to analyze the assertion and reason provided in the question step by step.

### Step 1: Understanding the Assertion
The assertion states that:
1 amu (atomic mass unit) = \(1.66 \times 10^{-24}\) grams.

### Step 2: Understanding the Reason
The reason states that the actual mass of one atom of Carbon-12 (C-12) is equal to \(1.99 \times 10^{-23}\) grams.

### Step 3: Calculation of the Mass of One Atom of C-12
We know that:
- One mole of Carbon-12 (C-12) has a mass of 12 grams.
- One mole contains \(6.022 \times 10^{23}\) atoms (Avogadro's number).

To find the mass of one atom of C-12:
\[ \text{Mass of one atom of C-12} = \frac{\text{Mass of one mole of C-12}}{\text{Number of atoms in one mole}} = \frac{12 \text{ grams}}{6.022 \times 10^{23}} \approx 1.99 \times 10^{-23} \text{ grams} \]

### Step 4: Calculation of 1 amu
The definition of 1 amu is:
\[ 1 \text{ amu} = \frac{1}{12} \times \text{mass of one atom of C-12} \]
Substituting the mass of C-12:
\[ 1 \text{ amu} = \frac{1}{12} \times (1.99 \times 10^{-23} \text{ grams}) \approx 1.66 \times 10^{-24} \text{ grams} \]

### Step 5: Conclusion
Both the assertion and the reason are true:
- The assertion is correct as \(1 \text{ amu} = 1.66 \times 10^{-24}\) grams.
- The reason is also correct as the mass of one atom of C-12 is \(1.99 \times 10^{-23}\) grams.

However, the reason does not correctly explain the assertion since it does not directly relate to the definition of 1 amu.

### Final Answer
Both the assertion and reason are true, but the reason is not a correct explanation of the assertion. Therefore, the correct option is B.

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