Calculate the molarity of a solution containing $5g\text{of}NaOH\text{in}450mL$ solution.

Moles of $NaOH$
Given:
Mass of $NaOH=5g$
And volume of solution $=450mL\text{or}450\times {10}^{-3}L$
Molar mass of $NaOH=23+16+1=40gmo{l}^{-1}$
Moles of $NaOH=\frac{\text{mass of}NaOH}{\text{molar mass of}NaOH}$

Moles of $NaOH=\frac{5g}{40gmo{l}^{-1}}=0.125mol$

Molarity of solution
We know,
Molarity =$\frac{\text{Mole of solute}}{\text{Volume of solution (L)}}$

So,
Molarity $=\frac{0.125mol}{450\times {10}^{-8}L}$
$=0.278mol{L}^{-1}or0.278M$