Explanation:
Molality is the ratio of the amount of substance of a solute (in moles – n) to the mass in kilograms of the solvent (m).
The symbol for molality is usually W and it can be calculated by the following formula:
W = n/m
here, we need to calculate n of NaCl using the formula:
n = m/MM
where MM of NaCl is 58.5 g/mol
n = 120/58.5
n = 2.05 moles
W = 2.05/30
W = 0.068 mol/Kg
Answer: A) 0.068
