A mixture of NH3 and NH4Cl will form a basic buffer.
pH of final solution =8.26
pOH of final solution=14−8.26 =5.74
Let the number of moles of NH4Cl added to 1L solution of be x.
Using Henderson’s equation.
pOH=pKb+log[NH3][NH4Cl]
5.74=4.74+log0.2x
∴x=2
The amount of ammonium chloride to be dissolved by the student in 0.2M ammonia solution to make one litre of buffer=2×53.5=107g