In an open tube, free surface of mercury remains

ANS:C - curved downwards

In an open tube, the free surface of mercury remains: Curved downwards. When mercury is placed in an open tube, its free surface forms a meniscus, which is the curved surface at the top of the liquid column. The shape of the meniscus depends on the adhesive and cohesive forces between the mercury molecules and the tube material. For mercury in a glass tube, the meniscus curves downwards. This occurs because the adhesive forces between mercury and glass are stronger than the cohesive forces within the mercury itself. As a result, the mercury is attracted to the glass surface, causing the meniscus to curve downwards.