Q.(i) Write any two similarities between Lithium and Magnesium.

Li and Mg show a diagonal relationship, so they resemble each other more than Li resembles the other alkali metals: both form nitrides directly and both give only the normal oxide (never peroxide) on combustion. Biologically, Na⁺ regulates nerve impulses and fluid balance, while Ca²⁺ builds skeletal structure and enables muscle contraction/clotting.

(i) Two similarities between Lithium and Magnesium.

Lithium (Group 1) and Magnesium (Group 2) show a "diagonal relationship" due to similar charge/size ratios (ionic radii and polarising power are comparable). Two genuine similarities:

1. Both react directly with nitrogen gas (N2) on heating to form ionic nitrides — Li forms Li3N and Mg forms Mg3N2 — unlike other alkali metals (Na, K, etc.), which do not react directly with N2 this way.
2. Both form only the normal oxide when burnt in air/oxygen — Li2O and MgO respectively — rather than a peroxide or superoxide, unlike heavier alkali metals (Na forms Na2O2, K forms KO2). (Other valid similarities: both carbonates decompose on heating to the oxide + CO2 at relatively low temperature; LiCl and MgCl2 are both covalent/deliquescent; fluorides and carbonates of both are only sparingly soluble in water.)

(ii) Biological importance of sodium and calcium. …