The correct option is D Fall down
In a barometer, there is a vacuum above the mercury column, and consequently, there is no force acting on the mercury from the top. The atmospheric pressure only acts from beneath the tube and is balanced by the gravitational force. Now, if a hole is drilled at the top of the tube then vacuum will no longer exist. So, the atmospheric pressure will start acting over the mercury from above and below will balance each other and the gravity will pull the column down.