Which of the following has a maximum number of atoms?
18g of CH4 contains a maximum number of atoms.
Molar mass of CH4 = The atomic mass of C + 4 X the atomic mass of H
= 12 + 4
= 16g
Number of atoms = 1 + 4 = 5
Thus,
Number of atoms = Number of atoms in the molecule×
= 
= 5.63 NA
The number of atoms in 18g of H2O :
Molar mass of H2O = 18g; Number of atoms = 2 + 1 = 3
= 
= 3 NA
The number of atoms in 18g of O2:
Molar mass of O2 = 32g; Number of atoms in O2 = 1 + 1 = 2
= 
= 1.12 NA
The number of atoms in 18g of CO2 :
Molar mass of CO2 = 44g;
= 
= 1.23 NA
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