The correct option is
D equipment
Option D: Nouns are words that name people, things, places,
animals, etc. In the given sentence, 'equipment' names 'necessary items used for a particular purpose'. For example, the equipment in a bakery includes a mixer, an oven, etc.
Hence the word is a noun and option D is correct.
Option A: Verbs are words that express an action.
Phrasal verbs are phrases formed with a verb and a particle and /or a preposition to form a meaning different from the individual words.
'Get rid of' is a phrasal verb that means 'to remove' or 'dispose of'. It names an action and not a thing.
Option B: 'Unwanted' is an adjective. Adjectives modify nouns.
Option C: 'Let's' is a contraction of 'let us'. 'Let' is a verb and 'us' is a pronoun. Pronouns refer to nouns that have been mentioned before, or the first person point of view.
Hence these words are not nouns and options A, B and C are wrong.