Question

Element $A$ reacts with oxygen to form a compound $A_2{O}_3$. If 0.359 gram of $A$ reacts to give 0.559 gram of the compound, then atomic weight of $A$ will be:

• A. 51
• B. 43.08
• C. 49.7
• D. 47.9

Answer 1

The correct option is B 43.08

Let atomic mass of element $A$ be =a g/mol

Again atomic mass of oxygen = 16 g/mol

So molar mass of the compound $A_2{O}_3=(2a+48)g/mol$

One molecule of the compound $A_2{O}_3$ Contains 2 atoms.

So the ratio of mass of $A$ and $A_2{O}_3$ in a molecule $\frac{2a}{2a+48}$

Again it is given that 0.359 grams of $A$ reacts to give 0.559 grams of the compound. So we can write

=>$\frac{2a}{2a+48}=\frac{0.359}{0.559}$

=>$\frac{a}{a+24}=\frac{359}{559}$

On solving, $a=43.08$

So, the correct option is $B$