Question

The ratio by mass of hydrogen and oxygen atoms in a water molecule is:

• A. $1:2$
• B. $1:8$
• C. $2:1$
• D. $1:16$

Answer 1

The correct option is B $1:8$

Chemical formula of water is $H_{2}O$.
Mass of $H$ atom is $1\text{u}$
Mass of $O$ atom is $16\text{u}$.
Hence the ratio by mass $H:O=2:16=1:8$