Could you check if all these sentences sound natural? In some of them I have included a few versions because I coudn't choose which one was the best option.

This doctor is often sent for.

He is always met by his friends at the station.

Are you given books to read in school?

The captives were led to/in a huge lounge/hall.(I think either to or in are correct)

What kind of exercises have been done in the classroom?

Many schools will be built next year.

This work will be done/finished/made next week.

Will this work be done next week?

He is laughed at by everyone.

When were these apple-trees planted?

He was often remembered and talked about at the institute.

He was remembered and talked about often at the institute.

He was remembered and talked about at the institute often.

Often he was remembered and talked about at the institute.

1. This is grammatically okay, but as for naturalness, it is not something that you would often hear in the US - the passive voice is a "weaker" voice and in a strong statement like this you'd generally want the active voice. You'd probably hear something more like: "This doctor is much in demand and many people ask for him."

2. This is grammatically okay, but again, the passive voice would not often be used in casual speech (the passive is typically used in academic work, lab reports, etc., and in situations where you need to be careful of what you say, like law enforcement and the legal system). You'd probably want to say it something like: "His friends always meet him at the station."
3. This is okay grammatically, but again, the passive voice is usually awkward in conversation. In casual speech you'd probably want to say: "Do they give you books to read in school?"

4. This is okay. This is not conversation, and the passive is fine here: "The captives were led to a huge hall."

5. This is okay. In an academic environment the speech is typically more formal than in casual conversation, and you might hear things like this, say, between the principal and a teacher - but this is very formal, stuffy speech even for academia. In casual speech between two teachers outside of school you'd likely hear: "What kind of exercises do you do in the classroom?"

6. This is okay. In a formal government report the passive might be used like this.

7. This is okay. In construction contracts the passive might be used like this: "This work will be finished next week."

8. Okay. Again, construction contract-type talk: "Will this work be finished next week?"

9. Grammatically okay but in casual speech the passive is awkward. You'd likely hear: "Everyone laughs at him."

10. Okay. This is passive, and rather formal for casual speech. You might hear instead: "When did you plant these apple trees?"
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11. Okay. You might see this in a novel, for example.

12. Okay.

13. Putting the adverb so far from the verbs it modifies is awkward. Put closer to the verbs.

14. Adverb is too far from its verbs. Put closer.