Which one is correct/most scientific?
Both are correct but have different meanings. Developing something for Android would mean that the application would eventually run on Android. Developing on Android would mean that you run development tools with Android in order to make your software.
Typically, part of the process for developing something for a platform involves using the platform itself, so for sort of implies the on. But using on wouldn't properly reference where you actually do most of your development: On a platform other than Android (such as Windows.)
The short answer is that the best choice is:
I am developing a certain application for Android
As for your other suggestions, they work best when the people you are talking to don't know what Android is. It is usually worded as such, however:
I am developing a certain application for the Android platform
In computing, platform typically comes after the relevant name:
Macintosh platform
Windows platform
iOS platform
I'd add something after Android:
I am developing a certain application for Android phones. I am developing a certain application for Android devices.
I agree with MrHen that "I am developing a certain application for Android" is the best choice of your original options. It's definitely correct. But I think that in practice, people aren't using Android by itself yet like they would for, say, mac or Windows.
Speaking as someone who actually does develop Android applications (for learning English, even: market.android.com/details?id=com.realpeopletalk), things I say are:
I'm developing an Android app. I'm working on an Android app. I've got an Android app that I'm working on. I write software for Android phones (usually said to non-technical people).
"I am developing a certain application for the Android platform."
Sounds a bit more preferable.
