IIT JEE Advanced 2009 Paper 2

We have
P−0V0 = P1V1 (1)
and the pressure at equilibrium is
P = P0−ρgh
=
= (98×103)N∕m2
Substituting in Eq. (1), we get
105 [A(500 − H)] = 98 × 103 [A(500 − 200)]
where A is the cross-section of water column.

Now, if H = 206 mm, we conclude that the level of water falls down by 6 mm. Hence, the correct answer is 6.