Final answer:
In the sentence 'The mall will be open this evening.', 'this' is a demonstrative adjective since it modifies the noun 'evening'. It does not function as a demonstrative pronoun because it does not stand alone replacing a noun.
Step-by-step explanation:
The question pertains to demonstrative adjectives and demonstrative pronouns. In the sentence 'The mall will be open this evening.', 'this' functions as a demonstrative adjective because it is describing the noun 'evening' and telling us which evening the speaker is referring to. A demonstrative pronoun would stand alone representing a noun, but in this case, 'this' is attached to a noun, thus making it an adjective.
According to the rules of demonstrative pronouns and adjectives, when 'this', 'that', 'these', and 'those' are used to directly point out or identify a noun, they are adjectives. When they replace the noun and stand alone in the sentence, they are pronouns. Therefore, the term 'this' in the given sentence is an adjective, not a pronoun, as it is modifying 'evening'.