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# If $4{\text{g}}$ of ${\text{NaOH}}$ are contained in one deciliter of solution, its molarity would be:A.$4{\text{M}}$B.$2{\text{M}}$C.$1{\text{M}}$D.$1.5{\text{M}}$

Last updated date: 20th Jun 2024
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Hint: To find molarity, we need to calculate moles of solute present in per litre of the solution. Moles of a substance is a SI unit of amount of substance, it can be calculated from mass, volume and number of a substance.

In order to find molarity of ${\text{NaOH}}$ or sodium hydroxide, we need to first find moles of sodium hydroxide present in the given volume of solution. As the given mass of sodium hydroxide is $4{\text{g}}$ and as molar mass of sodium hydroxide means mass of 1 mole sodium hydroxide molecules and that is $40{\text{g}}$ , from this data we can easily calculate moles of sodium hydroxide and moles of a substance can be given as:
${\text{no of moles}} = \dfrac{{{\text{given mass}}}}{{{\text{molar mass}}}}$ ,
putting values of mass of sodium hydroxide given and molar mass of sodium hydroxide.
We get, number of moles of sodium hydroxide as: ${\text{no of moles}} = \dfrac{4}{{40}} = 0.1{\text{mol}}$ .
Now volume of the solution can be determine from the given data in question as it is given that ${\text{NaOH}}$ are contained in one deciliter of solution, it means volume of solution is $0.1{\text{L}}$ .
Now molarity of the solution is defined as the number of moles of a solute present in $1{\text{L}}$ or $1000{\text{mL}}$ of the solution. In our case, solute is sodium hydroxide, thereby molarity of the solution can be given as:
${\text{Molarity}} = \dfrac{{{\text{moles of NaOH}}}}{{{\text{Volume of solution}}\left( {{\text{in L}}} \right)}} = \dfrac{{0.1}}{{0.1}} = 1{\text{M}}$ .

Thus, the correct option is C.

Note:
Molality of a solution is defined as the number of moles of solute present in $1000{\text{g}}$ or $1{\text{kg}}$ of a solvent. Mole fraction is the ratio of number of moles of solute or solvent present in the solution and the total number of moles present in the solution of the substance.