The solubility of ammonium chloride in water at various temperatures is given below:
Temperature: 10°C 20°C 40°C 60°C 80°C
Solubility: 24 g 37 g 41 g 55 g 66 g
Solubility at 40C = 41g
Solubility = Solid dissolved in 100g of water in a solution
So, mass of ammonium chloride needed to make a saturated solution of ammonium chloride in 50 g of water = 41/2 = 20.5g