a
\(Molality = \frac{{No.\,of\,moles\,of\,solute}}{{Wt\,of\,solvent\,in\,kg.}}\)

\(Here,No.\,of\,moles = \frac{{Molecular\,mass}}{{Wt\,of\,solvent}}\,\)

                                                    \( = \frac{{180}}{{180}} = 1\)

\(\therefore \,Molality = \frac{1}{1} = 1\)

Hence assertion and reason, both are correct, and reason is the correct explanation of assertion