Question

Which of the following will have the highest number of neutrons at STP?

• A. $22.4\text{L}$ of $C{O}_2$
• B. $11.2\text{L}$ $N_2$
• C. $112\text{L}{H}_2$
• D. $89.6\text{L}$ $He$

Answer 1

The correct option is A $22.4\text{L}$ of $C{O}_2$

For calculating the number of neutrons, we must find the number of moles in each sample.
$\text{Moles of}C{O}_2=\frac{\text{given volume}}{\text{molar volume at STP}}=\frac{22.4}{22.4}=1\text{mole}$
$\text{Moles of}{N}_2=\frac{\text{given volume}}{\text{molar volume at STP}}=\frac{11.2}{22.4}=0.5\text{mole}$
$\text{Moles of}{H}_2=\frac{\text{given volume}}{\text{molar volume at STP}}=\frac{112}{22.4}=5\text{mole}$
$\text{Moles of}He=\frac{\text{given volume}}{\text{molar volume at STP}}=\frac{89.6}{22.4}=4\text{mole}$

1 molecule of $C{O}_2$ has $6+2\left(8\right)$ neutrons = 22 neutrons
Therefore, 1 mole of $C{O}_2$ will have $22N_A$ neutrons.
1 molecule of $N_2$ has 14 neutrons.
So, 0.5 moles will have $(0.5\times 14N_A)=7N_A$ neutrons.
Hydrogen molecule does not have any neutrons
1 molecule of $He$ has 2 neutrons.
So, 4 moles of $He$ will have $(4\times 2N_A)=8N_A$ neutrons