Or equally, Pl_3 (3 atoms of Plutonium) would be very hard to distinguish from PI_3 (Phosphorus Triiodide), especially in a sans-serif font. Pu seems like a go

Or equally, Pl_3 (3 atoms of Plutonium) would be very hard to distinguish from PI_3 (Phosphorus Triiodide), especially in a sans-serif font. Pu seems like a good call to me. If it also amuses 4-year olds, then so much the better.