In this question, the sentence is divided into three underlined parts labelled…

Concept

Some nouns in English are uncountable (mass) nouns: they name something seen as a single, undivided whole rather than as separate items. An uncountable noun has no plural form and is never written with a plural ‑s. “Furniture” is one such noun — it is the collective name for tables, chairs, beds and so on, so it stays singular: we say “some furniture” or “pieces of furniture”, never “furnitures.”

Applying it to this sentence

Test each underlined part for a grammatical error:

• “The old furnitures” — this adds a plural ‑s to an uncountable noun, which is not allowed. This is the error; it must read “The old furniture.”

• “was disposed of” — acceptable: “dispose of” is the correct phrasal verb for getting rid of something, and the singular subject “furniture” correctly takes the singular verb “was.”

• “and the new ones were placed” — acceptable: in this idiom “ones” stands for the implied countable “pieces (of furniture)” and agrees with the plural verb “were,” so this part raises no clear-cut grammatical error.

Cross-check

Replace only the faulty word with its correct form: “The old furniture was disposed of and the new ones were placed.” The single unambiguous mistake — the plural ‑s on an uncountable noun — sits in “The old furnitures.” Because a real error is present, “No error” cannot be the response.