`{:("List - I","List - II "),("(mixed in equal volumes)","(Nature of solution)"),((A)0.2 "M HCN" + 0.1 M "KOH", (P)"Strong base"),((B) 0.2 "M HCl" + 0.1 "M KCN", (Q)"basic buffer"),((C)0.2 M NH_(3) + 0.1 M HCl, (R)"acidic buffer"),((D) 0.2 M KOH + 0.1 M NH_(4) Cl,(S)" Strong acid"):}`

Answer

To solve the problem of matching the solutions in List - I with their corresponding nature in List - II, we will analyze each solution step by step.

### Step 1: Analyze Solution A (0.2 M HCN + 0.1 M KOH)
- **HCN** is a weak acid and **KOH** is a strong base.
- When mixed, they undergo a neutralization reaction:
\[ \text{HCN} + \text{KOH} \rightarrow \text{KCN} + \text{H}_2\text{O} \]
- Initial concentrations:
- HCN: 0.2 M
- KOH: 0.1 M
- After mixing in equal volumes, the concentrations become:
- HCN: 0.1 M (0.2 M diluted to half)
- KOH: 0 M (completely reacted)
- KCN: 0.1 M (produced from the reaction)
- The final solution contains HCN and KCN, which forms an **acidic buffer**.
- **Match**: A → R

### Step 2: Analyze Solution B (0.2 M HCl + 0.1 M KCN)
- **HCl** is a strong acid and **KCN** is a salt of a weak acid (HCN) and a strong base (KOH).
- HCl will dissociate completely, and KCN will provide CN⁻ ions.
- The solution will be dominated by the strong acid (HCl).
- **Match**: B → S

### Step 3: Analyze Solution C (0.2 M NH3 + 0.1 M HCl)
- **NH3** is a weak base and **HCl** is a strong acid.
- The reaction produces NH4Cl:
\[ \text{NH}_3 + \text{HCl} \rightarrow \text{NH}_4\text{Cl} \]
- Initial concentrations:
- NH3: 0.2 M
- HCl: 0.1 M
- After mixing:
- NH3: 0.1 M (0.2 M diluted to half)
- HCl: 0 M (completely reacted)
- NH4Cl: 0.1 M (produced from the reaction)
- The final solution contains NH3 and NH4Cl, which forms a **basic buffer**.
- **Match**: C → Q

### Step 4: Analyze Solution D (0.2 M KOH + 0.1 M NH4Cl)
- **KOH** is a strong base and **NH4Cl** is a salt that can release NH4⁺ ions.
- The KOH will dissociate completely, and NH4Cl will provide NH4⁺ ions.
- The solution will be dominated by the strong base (KOH).
- **Match**: D → P

### Final Matches:
- A → R (acidic buffer)
- B → S (strong acid)
- C → Q (basic buffer)
- D → P (strong base)

### Summary of Matches:
- (A) 0.2 M HCN + 0.1 M KOH → (R) Acidic buffer
- (B) 0.2 M HCl + 0.1 M KCN → (S) Strong acid
- (C) 0.2 M NH3 + 0.1 M HCl → (Q) Basic buffer
- (D) 0.2 M KOH + 0.1 M NH4Cl → (P) Strong base