c
\(2 \mathrm{M}\) solution of \(\mathrm{NaOH}\) means 2 mole \(\mathrm{NaOH}\) is present in \(1 \mathrm{L}\) solution; density \(=1.28 \mathrm{g} / \mathrm{ml}\)

mass of solution \(=\) volume of solution \(\times\) density \(=1000 \times 1.28\)

\(=1280 \mathrm{g}\)

mass of solvent \(=\) mass of solution \(-\) mass of solute \(=1280-80\)

\(=1200 \mathrm{g}\)

molality \(=\frac{2}{1200} \times 1000=\frac{20}{12}=\frac{10}{6}=\frac{5}{3}=1.67 \mathrm{m}\)