CBSE Class 9 Answered

1 mole of carbon dioxide CO₂ is the heaviest among 1 mole of H₂O, NH₃ and CO.

Atomic mass unit is a quantity by which the molecular mass of a substance can be defined most precisely. It is the mass of one molecule of a substance. It is calculated by summing up the atomic masses of all the elements present in that particular molecule.

Here,

(a) The molecular mass of H₂O can be calculated as follows:

H₂O = 2 X 1 + 16 = 18 u

(b) The molecular mass of CO₂ can be calculated as follows:

CO₂ = 12 + 16 X 2 = 44 u

(c) The molecular mass of NH₃ can be calculated as follows:

NH₃ = 14 + 3 X 1 = 17 u

(d) The molecular mass of CO can be calculated as follows:

CO = 12 + 16 = 28 u

 Therefore, 1 mole of carbon dioxide CO₂ (44 u) is the heaviest among 1 mole of H₂O (18 u), NH₃ (17 u) and CO (28 u).