What is the lightest metal?
The lightest metal in the periodic table is lithium (Li) with atomic number 3 density 0.53 kg/L.
However, the metal with the highest strength to weight ratio is titanium (Ti).
Lithium metal is extremely soft (and highly reactive) and so is unusable for many applications, but one atom of Li weighs 1/7th of an atom of Ti.
Lithium is the lightest metal, but is too soft and chemically reactive to be used for the things most other metals are good for. Beryllium is the next lightest metal, but is too toxic for use near living things. Sodium is a relatively light metal, but like lithium is too soft and chemically reactive to be used for the things most other metals are good for. Magnesium is a light and strong metal that has…
Usually Aluminum is the lightest metal used for circulating currency. In the US, the lightest metal though is zinc for post-1982 pennies (except for a few trial cents made from aluminum which were melted down), however a lot of countries use aluminum (or have in the past) for circulating coinage such as the Japanese 1 yen coin.