Question

Select the incorrect sets of elements and their molecular mass.

• A. $O_2$ = 32 u, $C{O}_2$ = 44u
• B. $O_2$ = 16 u, $C{O}_2$ = 18 u
• C. $O_2$ = 32 u, $H_{2}O$ = 18 u
• D. $C{O}_2$ = 46 u, $H_{2}O$ = 16 u

Answer 1

Answer: (B), (D)

$C{O}_2$ = 46 u, $H_{2}O$ = 16 u

Molecular mass is the total sum of the atomic masses of the elements present in the compound.
Atomic mass of oxygen, carbon and hydrogen are 16 u, 12 u, and 1 u respectively.

$$\begin{array}{cc}\text{Molecule}& \text{Molecular Mass}\\ O_2& 2\times 16\text{= 32 u}\\ C{O}_2& 12+2\times 16\text{= 44 u}\\ H_{2}O& 2\times 1+16\text{= 18 u}\end{array}$$
Hence, the molecular mass of oxygen molecule is $32$ u, the molecular mass of carbon dioxide is $44$ u and the molecular mass of water is $18$ u.