Question

If $n$ atoms of elements A weigh $15g$ and $4n$ atoms of elements B whose atomic weight is $30u$, weigh $45g$, then determine the atomic weight of A:

• A. $15u$
• B. $40u$
• C. $45u$
• D. $30u$

Answer 1

The correct option is B $40u$

Solution:- (B) 40 u

Let the atomic weight of element A be x u.

Given that 'n' atoms of elements A weigh 15g.

$\therefore n\times x=15g..........\left(1\right)$

Also given that 4n atoms of element B weigh 45 g and the atomic weight of element B is 30 u.

$\therefore 4n\times 30=45$

$\Rightarrow 120n=45$

$\Rightarrow n=\frac{3}{8}$

Substituting the value of n in ${eq}^n\left(1\right)$, we have

$\frac{3}{8}\times x=15$

$\Rightarrow x=15\times \frac{8}{3}$

$\Rightarrow x=40u$

Hence, the atomic weight of element A is 40 u.