Question

The density of a liquid is $1.2gmm{l}^{-1}$ . There are $35$ drops in $2ml$ . The number of molecules in one drope is :(Given mol. wt. of liquid $=70$ & $N_A=$ Avgadro's number)

• A. $\frac{1.2}{35}\times N_A$
• B. ${\left(\frac{1}{35}\right)}^2\times N_A$
• C. $\frac{1.2}{{\left(35\right)}^2}\times N_A$
• D. None of these

Answer 1

Answer: (C)

$\because$ In $2ml$ , no. of drops $=35$
$\therefore$ Volume of $1$ drop liquid $=\frac{2}{35}$
mass of $1$ drop liquid $=\frac{2}{35}\times 1.2=\frac{2.4}{35}gm$
moles of liquid in $1$ drop $=\frac{2.4}{35\times 70}=\frac{1.2}{35\times 35}=\frac{1.2}{{\left(35\right)}^2}$
no. of molecules in $1$ drop $=\frac{1.2\times N_A}{{\left(35\right)}^2}$