Find the number of millimoles for 0.160 g sodium hydroxide.

The number of millimoles of sodium hydroxide in a $0.160$ g sample is determined by first calculating its molar mass.

The molar mass of NaOH is $22.99 + 16.00 + 1.01 = 40.00$ g/mol.

Converting mass to moles gives $\frac{0.160}{40.00} = 0.004$ mol.

Since $1$ mole equals $1000$ millimoles, the millimole quantity is $0.004 \times 1000 = 4$ mmol.