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Chemistry Question on Some basic concepts of chemistry

The number of molecules in 18 mg18 \,mg of water in terms of Avogadro number NN is

A

10−3N10^{-3}N

B

10−2N10^{-2}N

C

10−1N10^{-1}N

D

10 N10\,N

Answer

10−3N10^{-3}N

Explanation

Solution

Given, weight of water =18 mg=18×10−3g=18\,mg=18\times 10^{-3}g
∴\therefore Number of moles =weightmolar mass=\frac{\text{weight}}{\text{molar}\,\text{mass}}
=18×10−318=1×10−3=\frac{18\times 10^{-3}}{18}=1\times 10^{-3}
and number of molecules = no. of moles ×\times Avogadro number.
= 1×10−3×N=\,1\times 10^{-3}\times N =10−3N.=10^{-3}N.