XPS analysis of this element must be careful not to confuse it with a similar binding energy peak from zinc. Sodium, oxygen, and this element make up Graham’s salt. The Gutmann–Beckett method uses NMR spectroscopy of this element’s 31 isotope. A triphenyl derivative of this element is found in Vaska’s complex and can also be used to create ylides (“ILL-ids”) in the Wittig (10[2])reaction. Oxygen and this element can form anions designated as (10[1])ortho or pyro, and also forms a triprotic acid. Alongside nitrogen (-5[1])and potassium, fertilizers report the content of this element. For 10 points, name this element with red and white varieties used to light matches. ■END■ (10[1])