A

The shape of the liquid meniscus in a capillary tube is determined by the angle of contact (also known as the wetting angle) between the liquid and the solid surface of the tube. For a convex meniscus to form, the cohesive forces within the liquid must be stronger than the adhesive forces between the liquid and the solid surface of the tube. This occurs when the angle of contact is greater than 90°.

• If the angle of contact is greater than 90°, the liquid does not wet the surface, resulting in a convex meniscus.
• If the angle of contact is less than 90°, the adhesive forces dominate, causing the liquid to spread and create a concave meniscus.
• If the angle is equal to 90°, the meniscus will be flat.
• If the angle is equal to 0°, the liquid completely wets the surface, also leading to a concave meniscus.

Therefore, the liquid meniscus in a capillary tube will be convex if the angle of contact is greater than 90°.