To determine which compounds turn red litmus paper blue, we need to identify which ones produce a basic solution when dissolved in water. Red litmus turns blue in basic solutions (pH > 7).

Step 1: Analyze each compound to see if it undergoes hydrolysis to produce OH⁻ ions.

KCN: Potassium cyanide. K⁺ is from strong base KOH, CN⁻ is from weak acid HCN. So, CN⁻ hydrolyzes: $\mathrm{CN}⁻+H_{2}O\rightleftharpoons \mathrm{HCN}+\mathrm{OH}⁻$ . Basic. ✔️

K₂SO₄: Potassium sulfate. K⁺ from strong base, SO₄²⁻ from strong acid H₂SO₄. No hydrolysis. Neutral. ❌

(NH₄)₂C₂O₄: Ammonium oxalate. NH₄⁺ from weak base NH₄OH, C₂O₄²⁻ from weak acid H₂C₂O₄. Both ions hydrolyze, but NH₄⁺ hydrolysis (acidic) dominates over C₂O₄²⁻ hydrolysis (basic) because Ka for H₂C₂O₄ is larger than Kb for NH₄OH. Overall acidic. ❌

NaCl: Sodium chloride. Na⁺ from strong base NaOH, Cl⁻ from strong acid HCl. No hydrolysis. Neutral. ❌

Zn(NO₃)₂: Zinc nitrate. Zn²⁺ is a small, highly charged cation (acts as Lewis acid), hydrolyzes to produce H⁺: ${\mathrm{Zn}}^{2+}+H_{2}O\rightleftharpoons \mathrm{Zn}\left(\mathrm{OH}\right)+H^{+}$ . Acidic. ❌

FeCl₃: Ferric chloride. Fe³⁺ is highly charged cation, hydrolyzes to produce H⁺. Acidic. ❌

K₂CO₃: Potassium carbonate. K⁺ from strong base, CO₃²⁻ from weak acid H₂CO₃. CO₃²⁻ hydrolyzes: $\mathrm{CO}{}_3^{2-}+H_{2}O\rightleftharpoons \mathrm{HCO}{}_3^{-}+\mathrm{OH}⁻$ . Basic. ✔️

NH₄NO₃: Ammonium nitrate. NH₄⁺ from weak base, NO₃⁻ from strong acid. NH₄⁺ hydrolyzes: $\mathrm{NH}{}_4^{+}+H_{2}O\rightleftharpoons \mathrm{NH}{}_4\mathrm{OH}+H^{+}$ . Acidic. ❌

LiCN: Lithium cyanide. Li⁺ is from strong base LiOH, CN⁻ is from weak acid HCN. CN⁻ hydrolyzes to produce OH⁻. Basic. ✔️

Step 2: Count the basic compounds. They are: KCN, K₂CO₃, LiCN.

Final Answer: The total number is 3.

Related Topics and Formulae

Salt Hydrolysis: Salts can produce acidic, basic, or neutral solutions based on the strength of their parent acid and base.

• Strong acid + Strong base salt → Neutral (e.g., NaCl, K₂SO₄)
• Strong acid + Weak base salt → Acidic (e.g., NH₄NO₃, Zn(NO₃)₂)
• Weak acid + Strong base salt → Basic (e.g., KCN, K₂CO₃, LiCN)
• Weak acid + Weak base salt → Depends on relative Ka and Kb (e.g., (NH₄)₂C₂O₄ is acidic since Ka(oxalic) > Kb(ammonia))

Hydrolysis reaction for anion A⁻ from weak acid: $A⁻+H_{2}O\rightleftharpoons \mathrm{HA}+\mathrm{OH}⁻$

Hydrolysis constant: $K_h=\frac{K_w}{K_a}$