"Application for Android" versus "application on Android"

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

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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