A U-tube contains two immiscible non-reacting liquids. PA, PB, PC and PD are pressures at points A, B, C and D respectively. Then

If y be the height of a point in a liquid from the axis of the horizontal part of the tube and P be the pressure at that point, then dPdy=−ρg where ρ is the density of liquid. Liquid 1 is lighter than liquid 2. So up to the interface of liquids in the left arm, dPdy=−ρ2g is the same in both arms, hence PC=PD. But above the interface of liquids dPdy=−ρ1g in the left arm and dpdy=−ρ2g in the right arm. Since ρ1<ρ2, we can conclude PA>PB.