Question

Arrange the following in decreasing order of the number of molecules contained in: (A) 16 g of O$_2$, (B) 16 g of CO$_2$, (C) 16 g of CO, (D) 16 g of H$_2$

• A. (A), (B), (C), (D)
• B. (D), (C), (A), (B)
• C. (B), (A), (D), (C)
• D. (C), (B), (D), (A)

Answer 1

The Correct Option is B

To arrange the given substances in decreasing order of the number of molecules, we need to calculate the number of moles for each substance and then relate it to the number of molecules using Avogadro's number.

(A) 16 g of O₂

Molar mass of O₂ = 2 × 16 g/mol = 32 g/mol

Moles of O₂ = 16 g / 32 g/mol = 0.5 mol

Number of molecules = 0.5 mol × Avogadro's number (N_A)

(B) 16 g of CO₂

Molar mass of CO₂ = 12 g/mol + 2 × 16 g/mol = 44 g/mol

Moles of CO₂ = 16 g / 44 g/mol ≈ 0.36 mol

Number of molecules ≈ 0.36 mol × N_A

(C) 16 g of CO

Molar mass of CO = 12 g/mol + 16 g/mol = 28 g/mol

Moles of CO = 16 g / 28 g/mol ≈ 0.57 mol

Number of molecules ≈ 0.57 mol × N_A

(D) 16 g of H₂

Molar mass of H₂ = 2 × 1 g/mol = 2 g/mol

Moles of H₂ = 16 g / 2 g/mol = 8 mol

Number of molecules = 8 mol × N_A

Now, let's compare the number of moles:

H₂: 8 mol

CO: ≈ 0.57 mol

O₂: 0.5 mol

CO₂: ≈ 0.36 mol

Therefore, the decreasing order of the number of molecules is:

(D) > (C) > (A) > (B)

The correct answer is:

Option 2: (D), (C), (A), (B)