Cast iron is an alloy of iron and carbon, two elements that have atoms of very different sizes. this means that cast iron is likely a substitutional alloy an interstitial alloy a nonferrous alloy

Answer : Interstitial alloy

Explanation : Cast iron is an allow of iron and carbon, two elements that have atoms of very different sizes. It means that iron is likely to be the interstitial alloy.

As interstitial is an allow which sits in interstitial 'hole' between the atoms of different elements in a metal lattice of a compound.

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.