Android Commercial License problem

One question:

I have developed an android program for my client,
however they might not purchase source code,
in another round they would like to only purchase the .apk file that i have developed.

My question now is, what open source license is Android falls into? can i only sell apk file and keep my source code closed ? if it is not capable of closing source code, then what other options do i have to protect my code? what about marketing on play store? if i sell my apk on play store, do i have the liability to disclose my source as well? since it's open-source. Do my client have the right to take over the authority and re-sell?

Many thanks.

The license of the operating system (Android) generally has no effect on the licenses for the software that run on it (your app). Since you're not distributing the Android operating system with your apk, you're not bound by its license.

You can sell the binary without the source provided there are no other licensing conflicts. For example, if your app uses GPL code in it and you are distributing that GPL code then you would have to distribute the source code.

Thanks for the reply, what about with BSD license? is there any loss?

Below link is very helpful to fix your problem regarding Android Commercial License http://developer.android.com/license.html