Tafsir of Al-Muddathir 74:40

(In gardens) is the predicate of a deleted subject. The tanwin [nunation] is for the purpose of magnification, and the sentence is an initiation occurring as an answer to a question arising from what preceded it regarding the exception of the Companions of the Right, as if it were said: "What is their state?" So it was said: "They are in gardens whose essence cannot be fathomed nor can their description be attained."

It is permissible for the prepositional phrase to be in the position of a circumstantial qualifier (hal) for the Companions of the Right, or for their pronoun. In the saying of the Exalted, "Questioning one another," it is placed first for the sake of importance, while observing the verse ending. It is said [the meaning] is "for questioning."

The intention of their questioning is not that some of them ask others—such that each one of them is both a questioner and a respondent simultaneously—but rather the occurrence of the act of questioning from them, stripped of the other aspect. Although the tafa'ul form was originally laid down to indicate the issuance of an action from multiple parties and its occurrence upon them both, so that each one becomes both a subject and an object simultaneously—as in your saying "The people exchanged insults" (i.e., each one insulted the other)—it may be stripped of the second meaning, with the intention being only the first. The one upon whom the action occurs is something else, as in your saying "You see it, and we see it [together]."

Jar Allah [Al-Zamakhshari] said: "If the speaker is singular, he says 'I called him,' and if it is a group, 'We called out to him.' Its parallels are 'I threw it' and 'we exchanged throws [at it],' and 'I saw the crescent' and 'we looked at it [together].' This tafa'ul does not involve both sides."

Based on this, the object being questioned is deleted; I mean, the criminals. The estimation is: "They question the criminals about them," meaning they ask the criminals about their states. Thus, it was changed to what is in the Glorious Arrangement. It is also said: "They question one another..."