On which arm version cores android can run?
The main supported ARM cores are V7 based cores, such as Cortex-A series. And from Kitkat Andoird 4.4, the minimum requirement is 512MB RAM, armv7 processors and OpenGL ES 2.0 compatible GPU.
George is correct but some ARMv5 and v6 based SoCs (i.e. ARM9 and ARM11) can run older versions of Android.
Check out this List of devices: ARMv7, ARMv6, ARMv5 - xda-developers
Were you interested in specific minimum requirements for different versions of Android?