MCQ
$6.023 \times 10^{22}$ molecules are present in $10 \,g$ of a substance $'x'.$ The molarity of a solution containing $5\, g$ of substance ${ }^{\prime} x ^{\prime}$ in $2\, L$ solution is.......... $\times 10^{-3}$
- A$20$
- ✓$25$
- C$22$
- D$18$
✓
Answer
Correct option: B.
$25$
b
moles $=\frac{\text { number of molecules }}{6 \times 10^{23}}=\frac{\text { given mass }}{\text { molar mass }}$
moles $=\frac{\text { number of molecules }}{6 \times 10^{23}}=\frac{\text { given mass }}{\text { molar mass }}$
$\Rightarrow$ molar mas $=\frac{10 \times 6.023 \times 10^{23}}{6.023 \times 10^{22}}=100 g / mol$
$\Rightarrow$ molarity $=\frac{\text { moles of solute }}{\text { volume of } \operatorname{sol}^{n}(\ell)}=\frac{(5 / 100)}{2}$
$=0.025$
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