KEAM 2020 Physics and Chemistry Solved Paper

see you have 20 gram NaOH.
and molar mass of it is = 40 gram.
so no. of moles= 20/40 = 1/2mole.
now volume of solvent= 1250ml and density= 0.8 g/ml.
so mass of solvent= 0.8 x 1250= 1000 gram= 1 kg.
so molality= mole of solute/ mass of solvent in kg.
=1/2/1= 1/2 molal= 0.5 molal.