Answer: The comparison is in its correct form in the sentence "It is the tallest building in the world".
Step-by-step explanation: All the sentences provided want to express the idea that there is a building that represents the highest degree in terms of size. In that way, the correct thing is adding a superlative adjective in the sentence and not a comparative adjective. Therefore, as "taller" is a comparative adjective and "more tall" intends to express comparison, they are incorrect options. The superlative form of the adjective "tall" is "tallest" (and not "most tall"); therefore, the correct option is "It is the tallest building in the world".