How colourful is this botanical garden!

This botanical garden is very colourful is the correct answer.
Option 1: Is the botanical gardencolourful? - is a wrong answer since the meaning of this option has changed; it gives the appearance that the questioner is unsure whether the garden is colourful or not and is looking for an answer. As a result, this is an incorrect answer.
Option 2- This botanical garden is very colourful because the above statement is exclamatory, and when we transform an exclamatory sentence to a declarative sentence, the word 'how' is deleted and 'very' is added before the adjective (colourful). This botanical garden is very colourful retains the same meaning. Thus, this is the correct answer.
Option 3- This botanical garden is not colourful is a wrong answer because the word 'not' is used in the statement in a negative sense, while the speaker is asking how colourful the garden is. As a result, this option does not define or provide an equivalent meaning for the primary statement. Thus, this is an incorrect answer.