Answer:
molality=moles of solutekilograms of solvent
moles of NaOH=Weight of NaOHMass of NaOH=2540=58=0.625
kilograms of H2O=Weight of H2O1000=1001000=0.1
∴molality=moles of solutekilograms of solvent=0.6250.1=6.25m
Hence, the correct answer is 6.25