Question

The number of molecules of ethane (molar mass $=30$) present in 3 g of pure ethane is

• A. $6.023\times10^{23}$ molecules
• B. $6.023\times10^{22}$ molecules
• C. $6.023\times10^{21}$ molecules
• D. $6.023\times10^{20}$ molecules
• E. $6.023\times10^{19}$ molecules

Hint:

1 mole of any substance contains $6.023 \times 10^{23}$ particles.

Answer 1

The Correct Option is B

Step 1: Concept
Number of moles ($n$) = $\frac{\text{Given mass}}{\text{Molar mass}}$.

Step 2: Meaning
Number of molecules = $n \times N_A$, where $N_A$ (Avogadro's number) $\approx 6.023 \times 10^{23}$.

Step 3: Analysis
$n = \frac{3}{30} = 0.1$ moles.
Molecules = $0.1 \times 6.023 \times 10^{23} = 6.023 \times 10^{22}$.

Step 4: Conclusion
Hence, correct answer is $6.023 \times 10^{22}$ molecules.
Final Answer: (B)