ᶦᵐ ʲᵘˢᵗ ᵖᵘᵗᵗᶦⁿᵍ ᵃⁿ ᵃᶜᵃᵈᵉᵐᶦᶜ ᵠᵘᵉˢᵗᶦᵒⁿ ᶠᶦʳˢᵗ ˢᵒ ᶦᵗ ᵈᵒᵉˢⁿᵗ ᵍᵉᵗ ᵗᵃᵏᵉⁿ ᵈᵒʷⁿ
ᵃⁿʸᵒⁿᵉ ʷᵃⁿⁿᵃ ᵗᵃˡᵏ ᵗʰᵒᵘᵍʰˀ
An element that is unstable and decays of its own accord is _____.

a metal
a nonmetal
a rare earth element
a radioactive substance