Question

$6.02 \times 10^{20}$ molecules of urea are present in 100 mL of its solution. The concentration of solution is :-

• A. 0.1 M
• B. 0.02 M
• C. 0.01 M
• D. 0.001 M

Answer 1

Answer: (C)

0.01 M

Answer 2

${Number \, of \, moles = \frac{ number \, of \, molecules}{N_A} }$
$=\frac{ 6.02 \times 10^{20}}{6.02 \times 10^{23}} = 10^{-3} mol$
${ Molar \, conc = \frac{ n \times 1000}{V_{solution} (mL)} = \frac{10^{-3} \times 1000}{100}}$
Molar conc. = 0.01 M