# What is the molar quantity of a 0.40*g mass of sodium hydroxide?

As always we take the quotient: $\text{Number of moles"="Mass"/"Molar mass}$
i.e. $\text{Number of moles} = \frac{4 \cdot g}{40 \cdot g \cdot m o {l}^{-} 1} = 0.1 \cdot m o l .$