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How many molecules of water and oxygen atoms are present in 0.9g of water?

$\begin{array}{1 1}(a)\;3.010\times 10^{22}&(b)\;6.02\times 10^{23}\\(c)\;2.010\times 10^{23}&(d)\;4.01\times 10^{22}\end{array}$

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Gram-molecular mass of water=18g
Number of moles in 0.9g of water =$\large\frac{0.9}{18}$
$\Rightarrow 0.05$
Number of water molecules in one mole of water=$6.02\times 10^{23}$
Number of molecules of water in 0.05 moles
$\Rightarrow 0.05\times 6.02\times 10^{23}$
$\Rightarrow 3.010\times 10^{22}$
As one molecule of water contains one oxygen atom ,so number of oxygen atoms in $3.010\times 10^{22}$ molecules of water =$3.010\times 10^{22}$
Hence (a) is the correct answer.
answered Oct 22, 2013 by sreemathi.v

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