What is the lightest usable metal?

Answer 1

To a large extent, MAGNESIUM, element 12, is the lightest usable metal. Lithium (elmt. 3) and sodium (elmt. 11) are far too reactive to be used universally, and beryllium (elmt. 4) is very toxic and carcinogenic, thus magnesium is the lightest one that can actually be used. When powdered or shaved into small strips, magnesium is easily flammable, so in small quantities, ALUMINUM, element 13, is the lightest. But in bulk form, magnesium is surprisingly difficult to ignite, thus it is actually quite usable. Magnesium has many attractive properties. The first is the answer to the question: it's light. The second is that it is strong, especially when alloyed with aluminum or titanium (elmt. 22). It is also very abundant in the Earth's crust (9th most abundant element). Last, but definitely not least, is that magnesium is not toxic. So the answer to your question is largely magnesium, but could also be argued aluminum.