Question

The atomic weight of an unknown element, in atomic mass units (amu), is approximately $20\%$ less than that of calcium. The atomic weight of calcium is $40$ amu. Which of the following best approximates the atomic weight, in amu, of the unknown element?

• A. $8$
• B. $20$
• C. $32$
• D. $48$

Answer 1

The correct option is C $32$

Given that, the atomic weight of an unknown element is $20\%$ less than that of calcium's atomic weight, which is $40$ amu.

To find out: Approximate atomic weight of the unknown element.

Let the atomic weight of the unknown element be $x$ amu.

$\therefore x=40-20\%of40$

$\Rightarrow x=40-\frac{20}{100}\times 40$

$\Rightarrow x=40-\frac{1}{5}\times 40$

$\Rightarrow x=40-8=32$

Hence, the atomic weight of the unknown element is $32$ amu.