Which of the following has maximum number of atoms ?
20172021
Which of the following has maximum number of atoms ?
Answer: A. 16 g of CH4 — The number of atoms present in a given mass of a substance follows directly from the mole concept: number of moles = given mass ÷ molar mass, and total number…
- A.
16 g of CH4
- B.
16 g of CO2
- C.
16 g of O2
- D.
16 g of N2
Show answer & explanation
Correct answer: A
The number of atoms present in a given mass of a substance follows directly from the mole concept: number of moles = given mass ÷ molar mass, and total number of atoms = number of moles × atoms per molecule × Avogadro's number (NA). So, for a FIXED mass, the atom count is governed by the single ratio atomicity ÷ molar mass: a LOW molar mass (more moles from the same mass) raises it and a HIGH atomicity (atoms per molecule) raises it, and either factor can compensate for the other. The substance with the LARGEST value of this ratio yields the most atoms.
Applying this to 16 g of each gas given in the options:
Compound | Molar Mass (g/mol) | Moles (= 16 / M) | Atoms per Molecule | Total Atoms (× NA) |
|---|---|---|---|---|
CH4 | 16 | 1 | 5 (1 carbon + 4 hydrogen) | 5 |
CO2 | 44 | 16/44 ≈ 0.36 | 3 (1 carbon + 2 oxygen) | ≈ 1.09 |
O2 | 32 | 0.5 | 2 | 1 |
N2 | 28 | 16/28 ≈ 0.57 | 2 | ≈ 1.14 |
Cross-check: among the four gases, CH4 alone combines the lowest molar mass (16 g/mol) with the highest atomicity (5 atoms per molecule). Since both factors favour CH4 at once, its atom count must exceed every other row in the table even before the exact values are computed — this confirms the table above.
Hence, 16 g of CH4 contains the maximum number of atoms among the four given masses.