Question

Which is the lightest gas?

• A. ${\mathrm{N}}_2$
• B. $\mathrm{He}$
• C. ${\mathrm{O}}_2$
• D. ${\mathrm{H}}_2$

Answer 1

The correct option is D

${\mathrm{H}}_2$

Explanation for the correct option:

(D) ${\mathrm{H}}_2$

• The mass of the gases is used to determine how lightweight the gas is.
• This gas has no color or smell.
• Hydrogen is the lightest gas in the periodic table.
• The mass of hydrogen $\left({\mathrm{H}}_2\right)$ is $2\times 1$ or $2$grams.
• Among all the given gases, the mass of hydrogen is low. So, ${\mathrm{H}}_2$ is the lightest gas.

Explanation for the incorrect options

(A) ${\mathrm{N}}_2$

• This gas has no color or smell.
• The lightest element in group 15 of the periodic table is nitrogen.
• The mass of nitrogen $\left({\mathrm{N}}_2\right)$ will be $2\times 7$or $14$ grams.

(B) $\mathrm{He}$

• Helium $\left(\mathrm{He}\right)$ is the second lightest gas.
• The mass of helium $\left(\mathrm{He}\right)$ will be $4$ grams.

(C) ${\mathrm{O}}_2$

• This gas has no color or smell.
• After helium and hydrogen, it is the third most plentiful element in terms of mass.
• The mass of oxygen $\left({\mathrm{O}}_2\right)$ will be $2\times 8$ or $16$grams.

Therefore, the correct option is (D) . The lightest gas is ${\mathrm{H}}_2$.