Question

Which of the following samples contains the smallest number of atoms ?

• A. 1 g of $C{O}_2(g)$
• B. 1 g of $C_8{H}_{18}$
• C. l g of $C_2{H}_6(g)$
• D. 1 g of LiF(s)

Answer 1

Answer: (A)

(A) Molar mass of $C{O}_2=44gmo{l}^{-1}$
$44gC{O}_2\equiv 3\times 6.02\times 10^{23}$ atoms
$1g$ of $C{O}_2$ $=\frac{2\times 6.02\times 10^{23}}{4}$ atoms
$=0.068\times 6.02\times 10^{23}$ atoms
(B) Molar mass of $C_8{H}_{18}=114gmo{l}^{-1}$
$1g$ of $C_8{H}_{18}=\frac{26\times 6.02\times 10^{23}}{144}$ atoms
$=0.18\times 6.02\times 10^{23}$ atoms
(C) Molar mass of $C_2{H}_6=30gmo{l}^{-1}$
$1g$ of $C_2{H}_6=\frac{8\times 6.02\times 10^{23}}{30}$ atoms
$=0.27\times 6.02\times 10^{23}$ atoms
(D) Molar mass of LiF $=7\times 19=26$
$1g$ of LiF $=\frac{2\times 6.02\times 10^{23}}{26}$ atoms
$=0.077\times 6.02\times 10^{23}$ atoms
Clearly $(A)$ has minimum number of atoms