Should I inform the graduate admissions committees (of all the Universities I have applied to) of the acceptance of one of my papers? I think if it was a standalone question then the answer would be an unequivocal "Yes". So I will present you my situation: while applying to graduate school I had mentioned that two of my papers are under submission at 2 different conferences (I had given the names of the conferences as well). One of them got accepted today and the other one was rejected a few days back. 

Now the thing is, I feel that informing them about the acceptance might increase my chances considering this is my first paper and I'm an undergrad currently (is this a myth?). But the issue is, if I inform the committees about the accepted paper alone then I feel guilty about the fact that I'm deliberately concealing information about the rejected paper. And if I don't, I feel I might not be making any use of the fact that the paper got accepted somewhere. 

Can someone tell me what could be done?
Ben Norris' comment is right.  I will elaborate a bit.

As an undergrad, having an accepted paper is much more significant than having a rejected paper (i.e., the net perception is very positive even if they learn about both).  Furthermore, rejection is probably temporary (you'll probably resubmit after improving it and it may get accepted) whereas acceptance is permanent.

Tell them about the acceptance.  If they ask directly, tell them about the rejection.  But there is no reason to feel obligated to broadcast a paper's rejection.  The people reviewing your application certainly don't list their paper rejections when they apply for a job or a grant!