Q. The number of water molecules present in a drop of water (volume 0.0018 mL) at room temperature is
A) $6.023 \times 10^{19}$
B) 1.084$\times 10^{18}$
C) 4.84$\times 10^{17}$
D) 6.023$\times 10^{23}$
Explanation
(a)
Number of moles $= \frac{weight}{olecular\ wt.} = \frac{0.0018}{18} \times 1 \times 10^{- 4}$
[$\because 0.0018\ mL = 0.0018\ g$]
$\therefore$ Number of water molecules $= 1 \times 10^{- 4} \times 6.02 \times 10^{23}$
$= 6.023 \times 10^{19}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.