I was just curious to know whether the scientific articles and review published in preprint repository like bioRxiv are citable? If yes, is it good practice to do that since mostly such articles are not peer-reviewed?
this is your personal decision whether to cite preprints. In my opinion if you found them inspiring then you should cite them. This is all about Open Science.
It is most likely that good preprint will be published. There are possibilities to cite a given article in general - not pointing the preprint version nor the published version that can appear in the future, but thesis included by them in general.
This can be implemented by DOI versioning system (e.g. https://blog.zenodo.org/2017/05/30/doi-versioning-launched/) in many repositories.
I would recommend extreme caution. In the spirit of supporting good scientific evidence, we must only cite peer-review articles. Book chapters and authentic reports are in a different category and can be cited. We must not confuse “open science” with predatory publishing. Good open science dissemination happens through peer reviewed open access journals.
Citing only peer review papers we would have no chance to disseminate Albert Einstein contribution as he published only one paper (and it had a minor importance) in the peer-reviewed journal ;-)
We should not confuse predatory publishing with the publishing of preprints as there are many journals commonly considered as predatory that using peer review anyway. On the other hand, citing a given preprint and having a former proofed contribution to a given field we could give more credibility to that preprint than a "blind peer-reviewer of unknown specialty".
This is not against peer-reviewing. Most of my papers are published in this way. This is only about not rejecting citing of preprints.
You should "peer review" any article you cite! There are wrong statements in "peer reviewed" articles as well. There could be excellent pre-prints too. The peer review process is not an exact science. You could also check the comments on pre-print articles. These comments are also a form of peer review. Remember, we should all be peer reviewers.