i am doing my BS in chem engg.. can i take pure chemistry(physical) for my masters??

You should contact the universities you want to apply to and ask them directly. My own feeling is that a degree in chemical engineering should be fine. I know people with degrees in chemisty and engineering that have completed masters degrees in physics, so some range is allowed. Again, contact the universities yourself and ask.

It's probably a good start anyway. You may have to follow a few courses to catch up on a couple of topics. But that probably depends on which university you want to go to. As ajb said: the bets way to figure it out is to contact the chemistry faculty at the university you'd like to go to.

 

On a sidenote: there seems to be a bigger demand for chemical engineers than for chemists on the job market (but I am too lazy to find a link to back that up, so treat this as hearsay).