Answer:
Pronoun
Explanation:
In the sentence - This is a big mess. - 'this' is used as a pronoun, to be exact a demonstrative pronoun.
A demonstrative pronoun is a pronoun that is used to point at something specific within a sentence. It can be items in space or time.
These pronouns are This, That (for singular), These and Those (for plural).
This / These are used for singular items that are nearby. That / Those are used for multiple items that are not near us.
Examples:
This is my cat. - we can point at it, the cat is near us.
That is a plane. - the plane is not near us, so we use 'that'.
These are my favorite toys. - we point at many toys, and they are near us.
Those are my classmates. - we point at the classmates, they are not near.
Why 'this' is not a determiner in the sentence - This is a big mess.
A determiner is a word that introduces a noun. It always comes before a noun, not after or without a noun near!
This car is bad.
These pies look delicious.
I hope it helped you :)
