Question

Arrange the following in order of increasing mass
(i) $3.0115 \times 10^{23}$ molecules of white phosphorus
(ii) $10$ moles of gas
(iii) $1$ g molecule of anhydrous $Na_2CO_3$
(iv) $33.6 \,L$ of $CO_2$ gas at STP

• A. $ii < i < iv < iii$
• B. $iii > iv > i > ii$
• C. $i < ii < iv < iii$
• D. $i < iv < iii < ii$

Answer 1

Answer: (A)

(i) At. wt. of $P = 31$ and atomicity of $P$ is $4$
Mol. wt. of white $P = 31 \times 4 = 124$
$\therefore 6.023 \times 10^{23}$ molecules of white $P$ weigh $124\, g$
$\therefore 3.0115 \times 10^{23}$ molecules of white $P$ weigh
$\frac{124}{6.023} \times 3.015$
$ = 62\,g$
(ii) Wt. of $1$ mole of $H_2$ gas $= 2 \,g$
Wt. of $10$ moles of $H_2$ gas $= 2 \times 10 = 20 \,g$
(iii) $1\, g$ molecule of anhydrous $Na_2CO_3 =$ Mol wt. of $Na_2CO_3$ in $g = 106 \,g$
(iv) At STP $22.4 \,L \,CO_2$ weighs $44 \,g$
$\therefore 33.6\,L\,CO_2$ weighs $\frac{44}{22.4} \times 33.6\,g$
$ = 66\,g$
So, the correct choice
$ii < i < iv < iii$