If the diameter of the main reinforcement in a slab is 16 mm, the concrete cover to main bars is A. 10 mm B. 12 mm C. 14 mm D. 16 mm

The correct answer is B. 12 mm.

The concrete cover is the thickness of concrete that surrounds the reinforcement. It provides protection for the reinforcement from corrosion and fire, and it also helps to distribute the load evenly. The minimum concrete cover required for main reinforcement in a slab is 12 mm.

Option A is incorrect because the minimum concrete cover for main reinforcement in a slab is 12 mm.

Option C is incorrect because the minimum concrete cover for main reinforcement in a slab is 12 mm.

Option D is incorrect because the diameter of the main reinforcement is 16 mm, and the minimum concrete cover for main reinforcement in a slab is 12 mm.