Calculate the percentage composition of oxygen and hydrogen in Water ${\mathrm{H}}_2\mathrm{O}$.

Given : Atomic weight of H = 1u, O = 16u

Step 1: Given data

Atomic weight of H = 1u, O = 16u

Step 2: Finding the mass for the given data

The molecular mass of ${\mathrm{H}}_2\mathrm{O}$ = (Number of hydrogen atoms x atomic mass of hydrogen) + (Number of oxygen atoms x atomic mass of oxygen)

The molecular mass of ${\mathrm{H}}_2\mathrm{O}$ = $\left(2\times 1\right)+\left(1\times 16\right)$

The molecular mass of ${\mathrm{H}}_2\mathrm{O}$ = $2+16=18$u

Step 3: Finding the mass for each element

Mass of $\mathrm{H}$ = (Number of hydrogen atoms x atomic mass of hydrogen) $=\left(2\times 1\right)=2u$

Mass of $\mathrm{O}$ = (Number of oxygen atoms x atomic mass of oxygen) $=\left(1\times 16\right)=16u$

Step 4: Finding the % composition

% composition is the proportion by mass of each element present in a compound.

% composition of $\mathrm{H}=\frac{2}{18}=11.11\%$

% composition of $\mathrm{O}=\frac{16}{18}=88.89\%$

Thus, the percentage composition of hydrogen and oxygen in Water ${\mathrm{H}}_2\mathrm{O}$ is $11.11\%,\mathrm{and}88.89\%$respectively.