Use of “this” and “It”

Question

In te next sentence:

We use "this" only in the first question. The answer and the other questions use "it"

Is correct?

If the above is correct, then the following example:

- Is this a gull?
- no, it's not a gull
- what is it?
- it’s a duck
- what color is it
- it’s black and white

Without taking into account the above explained, the example would be the following:

- Is this a gull?
- no, this is not a gull
- what is this?
- this is a duck
- what color is this
- this is black and white

Which of the two examples is correct?

Answer 1

"This" is deictic: it identifies something by pointing at it. The pointing might not be physically extending a finger, it might just be looking at the thing, or even more abstract; but in principle your attention is being directed at the thing.

"It" is resumptive: it only makes sense if both parties in the conversation already know what is being talked about.

So your first dialogue is completely normal.

In your second dialogue, the first answer "No, this is not a gull" is possible, and would tend to imply that the answerer is at pains to identify this, as opposed to other things around. "It" would also have been possible.

In the rest of the dialogue, "It" would be normal, and the use of "this" would tend to suggest that the questioner is pointing at a different object each time. It is not impossible with your intended meaning, but it is unusual, and would suggest to me that there is something rather formal or artificial about the conversation. (I don't mean "formal" in the sense of "high society", but in the sense of "something very structured, almost ritual").

Answer 2

If the subject is unknown in a question, this is used to distinguish something in particular. It is familiar, which is why it is common in answers, when the subject of the question is the subject of the answer.

It or this can only be present in a sentence, or they can be mixed together:

Is this a clothing store? Yes, this is a clothing store.

Is this the right format for the assignment? Yes, it is the right format.

Is it the first option or the second option? It is the first option.

One thing about mixing it and this is that answering an it question with this is uncommon:

Is it a comedy or a drama? This is a drama.