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How many molecules of atoms of oxygen are present in 5.6litres of oxygen $(O_2)$ at NTP?

$\begin{array}{1 1}(a)\;3.01\times 10^{23}atoms&(b)\;2\times 10^{23}atoms\\(c)\;1.9\times 10^{23}atoms&(d)\;4\times 10^{23}atoms\end{array}$

1 Answer

We know that 22.4litres of oxygen at NTP contain $6.02\times 10^{23}$ molecules of oxygen.
So,5.6litres of oxygen at NTP contain=$\large\frac{5.6}{22.4}$$\times 6.02\times 10^{23}$ molecules.
$\Rightarrow 1.505\times 10^{23}$ molecules.
1 molecule of oxygen contain =2 atoms of oxygen
So,$1.505\times 10^{23}$ molecules of oxygen contain=$2\times 1.505\times 10^{23}atom$
$\Rightarrow 3.01\times 10^{23}atom$
Hence (a) is the correct answer.
answered Oct 23, 2013 by sreemathi.v

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