How significant is it to publish a scientific "review paper" in 6–10 impact factor journal? I have published my thesis to an international conference but it was not anything reputed. However, I do not have access to lab now. I have been asked to be a part of a review-paper writing team and a book-chapter writing team. I am not sure which will have greater impact during my admission in grad school and among researcher community.
This really depends on the field and the venue...
In my own field, book chapters are almost useless for your goals - they come in two flavors: those where already accomplished authors write reviews of a subject and are considered highly but are written by people who do not need an introduction, and those solicited by publishers looking for cheap content they can resell. There are other fields where book chapters are a pretty central part of publishing.
That said, review articles can be basically the same: those where established researchers convey their wisdom are highly respected, but typically the authors have sufficient credit already. In my area, an impact factor of 6-10 is pretty good, though also low for a journal that trades in the review arena: highly influential reviews in review journals get tens to hundreds (sometimes thousands) of citations, so those journals have inflated impact factors.
With the limited information you've provided, I'd assume the review article is better, if indeed the journal is a good journal and not somehow inflating an impact factor with false citations (not an uncommon thing). The more important advice I would offer is for you to check the specific circumstances with an advisor you trust. Your thesis advisor would be a good start.