When is a roman numeral most likely needed in the name of an ionic compound? a)when more than one polyatomic ion appears
b)when the anion is a polyatomic ion
c)when more than one cation is used in the formula
d)when the cation is a transition metal

Answer is: D) when the cation is a transition metal.

The Roman numeral shows the charge and the oxidation state of the transition metal ion.

For example, cobalt can form two chlorides, with charge of 2+ (cobalt(II) chloride - CoCl₂) and with charge 3+ (cobalt(III) chloride - CoCl₃).

Transition metals are elements in the d-block of the periodic table.

D) When the cation is a transition metal.

For example, FeCl2 - iron (II) chloride vs FeCl3 - iron(III) chloride.

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.