When rainwater falls on heated bricks, it distorts the shape of the bricks, and this phenomenon is referred to as:

Correct option is D

When rainwater falls on heated bricks, the sudden cooling causes thermal shock, leading to distortion or deformation of the brick shape. This specific defect in bricks is known as chuffs.
Why other options are incorrect
(A) Blisters → Caused by trapped gases during burning, forming surface swellings.
(B) Checks → Fine surface cracks due to uneven shrinkage.
(C) Spots → Local discoloration or patches on the brick surface.