How can we find out on which platform a website is hosted e.g. Linux or Windows etc. ?

Thanks

Find out who hosts the site and see what servers they use.

Also, check through pages on the site and see what kind of pages they are using.
If they are using PHP then it's a pretty good chance they are using Linux. If they are using ASP it would be windows.
If all the pages are html only then it would be harder to determine.

If they have demo accounts, login to them and check on the server info.

If you go to Whois Source (http://www.whois.sc/), then that should tell you the type of server that a particular website is hosted on.

www.netcraft.com

Just type the link on what is this website running and it should give you a general overview.