The liquid (mercury) meniscus in capillary tube will be convex if the angle of contact is

The shape of a liquid meniscus in a capillary tube is governed by the angle of contact $\theta$, defined as the angle between the tangent to the liquid surface at the point of contact and the solid surface, measured within the liquid.

For mercury in glass, the meniscus appears convex, indicating that cohesive forces within the liquid exceed adhesive forces between the liquid and solid. This corresponds to an obtuse angle of contact: $\theta > 90^{\circ}$.

$\therefore$ The correct option is A.