Question

Which of the following has minimum number of molecules ? *



(a)18 g of H2O

(B)16 g of O2

(C)32 g of CH4

(D)88 g of CO2

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Answer 1

Answer:

a) 18g of H20 has minimum no. of molecules!

Answer 2

Option B: 16 g of O₂ is the correct answer.

(The question incorrectly states the word "molecules" which should have been "atoms" as we count the number of atoms in a given molecule)

Given:

grams of molecule in options

To find:

number of atoms in a given mass of the molecule

Solution:

To find a number of atoms (in grams) in a given mass of molecule we have to apply the formula given below:

Number of atoms = $\frac{weight }{Molecular mass}$ ×6.023×10²³ × k    (k = number of atoms in the molecule)

Based on this formula we calculate the number of atoms in grams.

Option B: 16 g of O₂

Number of atoms = $\frac{16}{32}$ × 2 × Avagadro number (Na)

Number of atoms =$\frac{1}{2}$ × 2 x NA

Number of atoms = 1 NA

Option A: 18 g of H₂O

Number of atoms = $\frac{18}{18}$ × 3 x NA

Number of atoms = 3  NA

Option C: 32 g of CH₄

Number of atoms = $\frac{32}{16}$ × 5 x NA

Number of atoms = 10 NA

Option D: 88 g of CO₂

Number of atoms = $\frac{88}{44}$ × 3 x NA

Number of atoms = 6 NA

Hence, option B is correct because it has a minimum number of atoms which is 1 NA in 16 g of O₂.

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