Question

Calculate the mass percentage of carbon in urea $\left({\text{NH}}_2{\text{CONH}}_2\right)$.

• A. $20$
• B. $10$
• C. $26.6$
• D. $46.6$

Answer 1

The correct option is A $20$

The percentage composition of a compound is the percentage by weight of each element present in it.
Percentage of an element = (Total mass of the element in one molecule/ Molecular mass) $\times 100$

Atomic mass of carbon = $12\text{u}$
Molecular mass of urea $\left({\text{NH}}_2{\text{CONH}}_2\right)$ $=(2\times 14)+(1\times 12)+(1\times 16)$$+(4\times 1)=60\text{u}$

Mass percentage of carbon $=\frac{12}{60}\times 100=20\%$