I have a relay with rating 12V DC 240V AC 2A.
I want to control this relay with AC.
I want to know what AC voltage that can drive this relay ?
( I think 12V AC will not correctly.)
Most likely your relay has coil rated for 12Vdc and contacts rating 240Vac/2A ..
To drive it you wll need to connect a dc voltage between 10V and 14V ..
If you have ≈12Vac you can connect a diode - 1N4001 or similar (or a bridge rectifier) in series with the coil ..
If you use 12VAC you can use one bridge diode.
otherwise you can use one 9VAC transformer and bridge diode and
filtering capacitor (about 100-220uF), to drive relay.