Tabs opening automatically on chrome I have a MacBook air
On clicking on the search bar or any link, another tab is opened with some ad on it.

I tried to download things like adwcleaner etc., but I can find them only in .exe extension.
Check out The Safe Mac's website (http://www.thesafemac.com/arg-identification/) on how to remove adware from OS X and Safari. It sounds like you've got Conduit or some similar adware/malware that has attached itself to Chrome.