Why does a lemon kept in water appears to be of larger diameter than it’s actual size

A lemon in a glass of water appear bigger than its actual size is due to refraction of light".
Reason:
Light is refracted as it passes from water into air. And the refracted ray bends away from normal. Refraction of light ray depends upon the nature of material and curvature of surface.under the right conditions,refraction also creates a magnifying effect .
The magnification depends upon the distance between the lens and the image and between lens and object.
Here, Tumbler with water acts as convex lens which curves outward in the middle and can focus light rays to magnify object.
Thus, water in a curved containers can thus be great magnifiers.