Define Molarity. Calculate the molarity of a solution containing $5g$ of $NaOH$ in $500ml$ of solution.

Molarity $\to$ Molarity is the concentration of a solution expressed as the number of moles of solute per litre of solution.

$\text{Molarity}=\frac{\text{No. of moles of solute}}{{\text{Volume of solution}}_{\left(\text{in L}\right)}}$

Now,

Molecular mass of $NaOH=40g$

Given mass of $NaOH=5g$

No. of moles $\left(n\right)=\frac{\text{Given mass}}{\text{Molecular mass}}=\frac{5}{40}=0.125\text{mol}$

Volume of solution $\left(V\right)=500mL=\frac{500}{1000}=0.5L$

Therefore,

$\text{Molarity}=\frac{0.125}{0.5}=0.25M$

Hence the molarity of solution is $0.25M$.