Question

The density of a liquid is $1.2gmml^{- 1}$ . 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 $=\frac{1 . 2 \times N_{A}}{\left(35\right)^{2}}$