Question

$1.5$ moles of $O_2$ combine with $Mg$ to form oxide $MgO$. The mass of $Mg$ that has combined is:

• A. $72g$
• B. $36g$
• C. $24g$
• D. $94g$

Answer 1

Answer: (A)

$72g$

$2Mg+O_2\to 2MgO$

1 mole of $O_2$ combines with 2 moles of $Mg$.

1.5 mole of $O_2$ will combine with $1.5\times 2=3$ moles of $Mg$.

Atomic mass of $Mg=24g/mol$

Mass of $Mg=3mol\times 24g/mol=72g$

Hence, 1.5 mole of $O_2$ will combine with $72$ grams of $Mg$.

Hence, option $A$ is correct.