The minimum thickness of a flat slab is taken A. 13 cm B. $$\frac{{\text{L}}}{{32}}$$ for end panels without drops C. $$\frac{{\text{L}}}{{36}}$$ for end panels without drops D. $$\frac{{\text{L}}}{{36}}$$ for interior panels without drop E. All the above

The correct answer is: B. $\frac{{\text{L}}}{{32}}$ for end panels without drops

The minimum thickness of a flat slab is taken as $\frac{{\text{L}}}{{32}}$ for end panels without drops, where L is the clear span of the slab. This is to ensure that the slab is able to carry the loads imposed on it without buckling.

Option A is incorrect because it is the minimum thickness of a flat slab with drops. Option C is incorrect because it is the minimum thickness of a flat slab with drops for interior panels. Option D is incorrect because it is the minimum thickness of a flat slab without drops for interior panels. Option E is incorrect because it includes options A, C, and D, which are all incorrect.