The angle of contact at the interface of water-glass is 0°, Ethyl alcohol-glass is 0°, Mercury-glass is 140° and Methyliodideglass is 30°. A glass capillary is put in a trough containing one of these four liquids. It is observed that the meniscus is convex. The liquid in the trough is

It is given that the meniscus is convex. This means the angle is obtuse. This indicates that the liquid in the trough is mercury. This can also, be understood from the fact as: -

The surface is always perpendicular to the resultant force. Since the meniscus is convex, the resultant force is inside the liquid. That means that cohesive force is greater than adhesive force like in the case of mercury.