(i) NH₄Cl (strong electrolyte) ⇌ NH₄⁺ (high) + Cl^‒ (high)
    NH₄OH (weak electrolyte) ⇌ NH4 + (low) + OH‒ (low)
(1) When an acid is added, it gives H⁺ ions which combine with OH^‒ ions (from NH₄OH) to produce H₂O (weak electrolyte) in absence of OH^‒ ions NH₄OH dissociates more and maintains the pH.
(2) When an alkali is added, it gives OH^‒ ions which combine with NH₄⁺ ions (from NH₄Cl) to produce NH₄OH (weak electrolyte). NH₄OH dissociates partially and OH^‒ ions produced are not sufficient to increase the pH.

(ii) HCl ⇌ H ⁺ + Cl^‒ , H₂S ⇌ 2H+ + S^2‒
In the presence of HCl (strong electrolyte), the dissociation of H₂S (weak electrolyte) is suppressed due to the presence of common ion H+ [common ion effect] and less S^2‒ ions are produced. In analytical chemistry groups are formed in increasing order of Ksp, Cu²⁺ belongs to 2nd group while Zn²⁺ belongs to 4th group. The Ksp of CuS is low and hence [Cu²⁺][S^2‒ ] > K_sp, CuS gets precipitated. But Ksp of ZnS is high and hence [Zn²⁺][S^2‒] < Ksp, ZnS doesn’t get precipitated.

i) 

ii) Sp³d    
(iii) Linear

(i)NaOH + F₂ →NaF + NaFO + H₂O

(ii) H₂S + H₂S0₄ → S+ SO₂ + 2H₂O

(iii) 2KMnO₄ + KI+H₂O → 2MnO₂+2KOH+ KIO₃

H₂S is a gas at room temperature whereas, H₂O is liquid at room temperature because H₂O has a stronger dipole interaction. The ability o oxygen atom to pull electrons is greater than of sulphur such that oxygen is more electronegative than sulphur. Hence Hydrogen forms stronger bond with oxygen and thus H₂O exist in form of liquid.