Question

Consider the following statements:
(a) Molecular mass of $C{H}_{3}OH$ is $32u.$
(b) In $N{H}_3$, the ratio of $N$ and $H$ by mass is $14:3.$
(c) The formula mass of $CaC{l}_2$ is $111u.$
(d) Isotopes have same mass number.

Which of the above statements are correct?

• A. $\text{(a) and (c)}$
• B. $\text{(a), (b) and (d)}$
• C. $\text{(a), (b) and (c)}$
• D. $\text{(a), (c) and (d)}$

Answer 1

Answer: (C)

$\text{(a), (b) and (c)}$

a) Molecular mass of $C{H}_{3}OH=12+4\times 1+16=32u$. This is correct statement.

b) In $N{H}_3$, the ratio of $N$ and $H$ by mass is $14:3.$, This is correct statement.

c) Formula mass of $CaC{l}_2=40+2\times 35.5=111u$. This is correct statement.

d) Isotopes have the same atomic number but different mass numbers. For example ${}_6^{12}C$ and ${}_6^{14}C.$ Hence given statement is incorrect.

Hence, option $C$ is correct.