In which sentence 'nest is used as a noun? ?

The task asks to identify which sentence uses "next" as a noun. In the options provided, we need to analyze the role of "next" in each sentence.

Option A, "I shall tell you more about it in my next," uses "next" as a noun. Here, "next" refers to the next event or item in a sequence, implying something that will come after the current instance (like "my next email" or "my next conversation"). This usage classifies "next" as a noun because it represents an entity (the following occurrence) rather than describing a position or a relationship.

In contrast, Options B ("what next?"), C ("he was sitting next to her"), and D ("I shall see you next Monday") use "next" in different grammatical roles. In Option B, "next" is an adverb, questioning what will follow. In Option C, "next" functions as an adjective, describing the position of the subject relative to "her." Finally, in Option D, "next" again acts as an adjective, specifying which Monday is being referred to. Thus, Option A is the only sentence where "next" is clearly used as a noun, making it the correct choice.