The correct option is B strong
The word 'fragile' refers to something easily breakable or prone to damage.
Option A, broad refers to being wide.
Option B, tall refers to something of a great or more than average height.
Option C, strong refers to something able to withstand force and pressure.
Option D, heavy refers to something of great weight.
Thus, according to the meaning, the word 'strong' is the opposite of the word 'fragile'.