How do I set a limit number of participants in a survey? I need only 100 participants in this survey. I think it can be done in the quota section, but can someone please advise me practically how?

If you use a quota, the respondent has to answer at least one question to be screened out.
E.g. First question "Gender"
Then you set a quota on "Gender" with limit "100".

This way you get 100 completes and afterwards all responses are screened out.

1. On the first screen after "Quota / Add new quota" you enter some name for the quota, the limit and the text that is displayed to the respondents.
2. On the next screen (after you clicked "Save") you select the question and answer that affect this quota.

Remember: You can test quotas only in activated surveys.

Read here
manual.limesurvey.org/Survey_quotas#Add_new_quota

Joffm

By the way: You should set the limit a bit higher. You always have to exclude responses for quality reasons.

And also keep in mind that if you have many cocurrent people answering (which I doubt with a target of n=100, but hey...) if there are 99 completes and two people are in the questionnaire they will both be able to finish, because LS will only screen out when there are n=100 completes in the quota. So even with the quota set, you could end up with a couple more respondents than the n=100.