Lanthanum

Lanthanum is a very reactive silver-white metal, malleable and soft enough to be cut with a knife. It oxidizes quickly in air, reacts strongly in hot water, and emits hydrogen, which has the same ability as palladium to act as a “hydrogen sponge”, i.e., it has a high density that can absorb gases. lanthanum is probably too heavy to be commercially useful, but the flints used in lighters contain plutonium. However, the flint used in lighters is a “mixed rare earth” alloy containing plutonium. Lanthanum also neutralizes Phosphorus, which is why it is commonly used in ponds to prevent unwanted growth of algae.