Question

$3$ gm of Mg is burnt in a closed vessel containing $3$ gm of oxygen. The weight of excess reactant left is :

• A. $0.5$ gm of oxygen
• B. $1.0$ gm of oxygen
• C. $1.0$ gm of Mg
• D. $0.5$gm of Mg

Answer 1

Answer: (B)

$1.0$ gm of oxygen

$\underset{24g}{Mg}+\underset{16g}{\frac{1}{2}{O}_2}⟶MgO$

$1gm$ $Mg$ requires $\frac{16}{24}g$ oxygen

So, $3gm$ $Mg$ requires $3\times \frac{2}{3}=2gm$ of oxygen

So, $3gm$ $Mg$ and $2gm$ of oxygen reacted and $1gm$ of oxygen left.

Hence the correct option is B.