Correct option is (b) 0.5000 m
For explanation: Given,
Mass of NaCl, m = 58.5 g
Moles of NaCl, n = mass/molar mass
n = 58.5g/(58.5 g/mole) = 1 mole
Molality = moles of solute/mass of solvent (in kg)
Volume of solvent = 2000 ml = 2 L
Mass of solvent = volume x density = 2 L x 1 kg/L = 2 kg
Molality = 1 mole/2 kg = 0.5 molal.