Many thanks for your great help. I have some qustions as follows:

1) I can explain everything if you'll just give me a chance/an opportunity.

If you give me a chance/an opportunity to speak, I'll explain.
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The answers you gave here were that only 'chance' is correct. Why does 'opportunity' not work here in the two sentences?

2) I never get/have a chance/an opportunity to relax these days.
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Your said "get a chance" is my preference, but "opportunity" doesn't sound weird.
Do you mean we can use 'get a chance' or 'have a chance' or 'get an opportunity' or 'have an opportunity' here?

3) I'd like to take/seize this opportunity to thank you for all your hard work.
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What is the difference in meaning between 'take this opportunity' and 'seize this opportunity' here?

4) Denise never misses the chance/opportunity of a free meal.
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Your answer: Neither. Maybe "the opportunity to accept a ..."?

I got the example 'Denise never misses the chance of a free meal' from online dictionary. I don't know why 'chance' is not fine here? Do you think chance really doesn't work here?

5) If I had  a chance/an opportunity to become a university studednt, I would study as hard as possible.
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Does 'had an opportunity' here mean 'it's likely to happen' ?

6) You should take the chance (=use the opportunity) to travel while you're still young.

Can I use 'opportunity' instead of 'chance' here as in ...take the opportunity to travel... ?
Do the both mean the same?

Thanks.

Hi GG,
Many thanks again for your kind reply and help. However, I have some more questions:

1) Do you mean
"I never have a chance to..." and
"I never get/have an opportunity to..."
aren't natural to say so?

2)You said:"Seize is more agressive. Someone can give you an opportunity and you can then take it, but if you seize it, you may interrupt."

What do you mean by 'interrupt' here?

3)"You should take the chance to travel while you're still young."

'Take the chance' works in the above sentence, but doesn't work in the following sentence:

"I'd like to take this chance to thank you for all your hard work."

Could you please explain why 'chance' isn't fine here?

4)"He never misses a chance to acccept a free meal."
Does this sentence sound natural? Doese it mean the same as 'opportunity' if so?

5)"Would you give me a chance/opportunity to make it up to you?"

Are chance and opportunity both fine here? Do they mean the same?

6)"Not necessarily. It the situation is possible, that's all."

What does 'it the situation is possible' mean in your earlier post?

7)"The offer of a free trip round the world is the chance/opportunity of a lifetime."

Is there any difference in meaning between them?

8)"For many athletes, the Olympics is a once-in-a-lifetime opportunity/chance."

Do the both mean a time or situation which you can use to do something that you want to do? Are they interchangeable here?

Could you please check if chance and opportunity are fine in the sentences below? Could you please also explain the difference if they have?

9)Everyone will have an opportunity/chance to comment.

10)I was never given the opportunity/chance of going to college.

11)You’ll have the opportunity/chance to ask any questions at the end.

12)There was no opportunity/chance for further discussion.

13)At least give him the opportunity/chance of explaining what happened.

14)We won’t get another chance/opportunity of a holiday this year.

15)There will be a chance/opportunity for parents to look around the school.

Thank you very much.

Thanks!