Question

Which of the following pairs of gases contains the same number of molecules?

• A. \(11\,\text{g of } CO_2 \text{ and } 7\,\text{g of } N_2\)
• B. \(44\,\text{g of } CO_2 \text{ and } 14\,\text{g of } N_2\)
• C. \(22\,\text{g of } CO_2 \text{ and } 28\,\text{g of } N_2\)
• D. All the above pairs of gases

Hint:

Equal number of molecules means equal number of moles. Always compare: \[ \text{Moles}=\frac{\text{Mass}}{\text{Molar mass}} \] If moles are equal, the number of molecules will also be equal.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Same number of molecules implies same number of moles (Avogadro's Law).
Step 2: Detailed Explanation:
Molar mass of $CO_2 = 44$. Molar mass of $N_2 = 28$.
Option (A): Moles $CO_2 = 11/44 = 0.25$; Moles $N_2 = 7/28 = 0.25$. (Match)
Option (B): Moles $CO_2 = 1$; Moles $N_2 = 0.5$. (No)
Option (C): Moles $CO_2 = 0.5$; Moles $N_2 = 1$. (No)
Step 3: Final Answer:
Pair (A) has equal molecules.