The answer is C, A, B in that order.
Pressure = Density * gravity * height.
Let us look at these three substances and assume gravity is 9.8 m/s squared.
The Salt water has a density of 1029kg/m3, height of 0.2 meters.
Pressure of salt water will be 1029*9.8*0,2 = 2,016 p
Fresh water has a density of 1000kg/m3
Pressure of salt water will be 1000*9.8*0.2 = 1,960 pa
Mercury has density of 13,534kg/m3
Pressure of mercury will be 13534*9.8*0.05 = 6,631 pa
So mercury exerts the highest pressure even at only 5cm height.