when i install 2012 r2 .what happens if I choose 2008 r2 on vcenter . any problem on operation system ?
It will not cause any issues. Important requirement is that you need VMtools for it. If you choose the wrong OS in the configuration and install another OS, the VMtools will be installed for wrong OS.
It will also suggest wrong SCSI bus if you are explicitly not choosing the right one yourself. The point is, why would you are anyone do it? Even if it is done, bring the machine down and change it.
hardware version old ( v8 ) if i change hardware verision . can it changes ? how to i change right . just delete vm and new install right ?