Corrosion Question

[dm36415]

Please excuse my vernacular, but I was reading about air plugs, and since my airpump was removed by the PO I went to check if all my plugs were in.

Five of them looked fine, but I was shocked when I couldn't see one due to what appears to be white colored corrosion all around the exhaust(?) pipe for that cylinder, appearing to even go between that pipe and the engine.

Cause/Cure?