The number of molecules in $18 m g$ of water in terms of Avogadro number $^{'} N^{'}$ is:

10^{- 3} N

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10^{- 2} N

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10^{- 1} N

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10 N

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Solution

The correct option is A $10^{- 3} N$
Given, weight of water $= 18 m g = 18 \times 10^{- 3} g$

$∴$ Number of moles $= \frac{W e i g h t}{M o l a r m a s s}$
$= \frac{18 \times 10^{- 3}}{18} = 1 \times 10^{- 3} m o l e s$
Number of molecules $=$ Number of moles $\times$ Avogadro number

$= 1 \times 10^{- 3} \times N$

$= 10^{- 3} N$ .

Hence, option A is correct.

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The number of molecules in 18 mg of water in terms of Avogadro number ′N′ is:

The correct option is A 10−3NGiven, weight of water =18 mg=18×10−3g∴ Number of moles =WeightMolar mass =18×10−318=1×10−3 molesNumber of molecules = Number of moles × Avogadro number =1×10−3×N =10−3 N.Hence, option A is correct.

The number of molecules in $18 m g$ of water in terms of Avogadro number $^{'} N^{'}$ is: