which is the reason that ionic compounds are brittle?

the bonds between the anions and cations are weak and therefore easily broken.

a strong repulsive force is created when cations suddenly align.

they involve positive metal ions in a sea of delocalized electrons.

they share electrons, which makes the bond brittle.

I believe the answer  to your question is b

explanation: no but i do not usually comment

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.