Q.Give two differences in between Double Salt and Complex Salt. OR Give two fundamental differences in between Nucleoside and Nucleotide.

Double salts break apart completely into simple ions in solution (giving normal ion tests); complex salts contain a complex ion that stays intact in solution (failing the normal metal-ion test).

Difference 1 — Behaviour in solution:

A double salt, e.g. Mohr's salt FeSO4.(NH4)2SO4.6H2O or potash alum KAl(SO4)2.12H2O, dissociates completely in water into all its simple constituent ions (Fe2+, NH4+, SO4^2- for Mohr's salt), each of which gives its characteristic chemical test.

A complex salt, e.g. K4[Fe(CN)6] (potassium ferrocyanide), dissociates in water to give K+ ions and the complex ion [Fe(CN)6]^4-, but the complex ion itself does NOT further dissociate into Fe2+ and CN- ions. Hence it fails to give the usual test for Fe2+ (no blue colour with K3[Fe(CN)6], etc.) and gives only a very weak/no test for free CN-.

Difference 2 — Stability/existence:

Double salts are stable and retain their identity only in the crystalline (solid) state; once dissolved they lose that identity and behave as a simple mixture of ions. …