Whose and its possible answers

Whose milk is that?

a) It is the cat's milk.
b) It is its milk.--

Both are correct, aren't they?-- No, B is not correct with the given context.

I know that it is wrong to say:
c) It is its.
But why? Could you tell me please.- No, that is not necessarily wrong in appropriate context, though it is highly unlikely.

Whose milk is that?
It is its milk.

Mister MicawberNo, B is not correct with the given context.

Why not Mister Micawber? I'm refering to the cat's milk, aren't I?

'Its' is the possessive adjective and 'milk' is the common noun.

There is no cat in the given context.

Mister Micawber,

Sorry, I forgot to mention that the students have a drawing with a cat a plate with milk in it.

I see no grammatically reason why you cannot say 'It is its', just as you could say 'It is hers/his/ours'. It sounds odd and is unused merely because we normally use 'it' of inanimate objects, not unsexed animals, and we do not normally use the Anglo-Saxon genitive for inanimate objects.

Thank you very much Mister Micawber.