IMAC A1225

my IMAC A1225 drive crashed without any back-up to restore to and no original OS, which OS can I buy from Apple store to do the install..

I have another OS that won't let me install it on this machine..

any help please?

here are the specs of my IMAC

Model identifier: IMAC9,1

Processor: Intel Core 2 Duo

serial Number: QP*****0TM

Thanks all

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