Leslie's Oxidizer II (old)

I just finished refilling my pool after some plaster repair, and am currently in the process of balancing. As I was doing chemistry inventory in the storage shed, I found a large supply (3 lbs.) of Leslie's Oxidizer II. It's probably about 10 years old. When it comes time to shock the pool in the spring, will this still work? Could it actually do any harm? If I can't use it, is there a proper disposal method?

Thanks,
Steve W.
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17K gallon Gunite

I'd never use that stuff even if it was new. 10 years old? Pitch, but I don't know how.