can I use AirPlay mirroring with IMac OS X Lion 10.7.5?

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Unfortunately not.

AirPlay Mirroring requires a second-generation Apple TV or later, OS X 10.8 or better and is supported on the following Mac models: iMac (Mid 2011 or newer), Mac mini (Mid 2011 or newer), MacBook Air (Mid 2011 or newer), and MacBook Pro (Early 2011 or newer). It also requires the computer to be using wi-fi.

Yes but it needs OS X 10.8 or better, you'd need to upgrade your operating system.