Question

Weight of crucible + weight of magnesium wire = X (before heating)
Weight of crucible + weight product magnesium oxide = Y (after heating)
Which of the following option is correct?

• A. X = Y
• B. X < Y
• C. X > Y
• D. Depends on element

Answer 1

Answer: (B)

Magnesium wire($Mg$) on heating in air gains weight due to the formation of magnesium oxide ($MgO$ ). It is shown by the following reaction.

$2M{g}_{\left(s\right)}+O_{2\left(g\right)}$ $⟶2Mg{O}_{\left(s\right)}$

So according to the law of conservation of mass, Mass of reactant = Mass of product.

So, $\text{Mass of magnessium wire + Mass of oxygen gas = Mass of magnesium oxide}$

$\therefore \text{X + Mass of}$ $O_2$ $=Y$

The above equation indicates that the mass of X is less than that of Y. i.e. $X<Y$

Hence, option $B$ is correct.