6.02×1020 molecules of urea are present in 100 mL of its solution. The concentration of urea solution is(Avogadro constant, NA=6.02×1023mol−1)

$6.02 \times 10^{20}$ molecules of urea are present in 100 mL of its solution. The concentration of urea solution is
(Avogadro constant, $N_{A} = 6.02 \times 10^{23} {mol}^{- 1}$ )

Amount of urea, $n = \frac{N}{N_{A}} = \frac{6.02 \times 10^{20}}{6.02 \times 10^{23} {mol}^{- 1}} = 10^{- 3} mol$

Concentration of urea solution, $c = \frac{n}{V} = \frac{10^{- 3} mol}{0.1 L} = 10^{- 2} {molL}^{- 1}$

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