Change the given sentence to an assertive sentence:
What a gorgeous gown!
A) This gown is gorgeous
B) It is a gorgeous gown.
C) Isn’t it a gorgeous gown?
D) Indeed, this is a gorgeous gown

Hint: Assertive sentences are those sentences that assert a sentence, facts, incidents, opinion, event, feeling, belief. Assertive sentences end with a period (.). Such as She likes to play badminton; We all are singing a song.

Complete answer:
Let us analyze the given options:
Option A) This gown is gorgeous – This option shows a feeling of great surprise and wonder or a feeling of amazement and astonishment. Therefore, this option cannot come under assertive sentences. Thus, this is an incorrect answer.
Option B) It is a gorgeous gown. – this option is an assertive sentence because this sentence ends with a period that is called full stop (.). Therefore, this is the correct answer.
Option C) Isn’t it a gorgeous gown? – this option does not show an assertive sentence. Therefore, this is an incorrect option because this option indicates a question being asked because this option ends with a question mark (?).
Option D) Indeed, this is a gorgeous gown – again this option shows a feeling of great surprise and wonder or a feeling of amazement and astonishment. Therefore, this option cannot come under assertive sentences. Thus, this is an incorrect answer.

What a gorgeous gown!
It is a gorgeous gown. (Option B)

Thus the correct answer is option ‘B’.

Note:
Declarative sentences are also known as assertive sentences as they provide information, facts or opinions. These sentences can be either affirmative or negative. For a better understanding of the sentence there are few examples:
1) His behaviour fascinates everyone.
2) Rohan likes ice cream
3) Allen plays badminton every alternate weekend.
Common things in all these examples are that they all are ending with a period that is also called as full stops (.).