The plot of pH-metric titration of weak base NH4OH vs strong acid HCl looks like which graph?

Step 1 — Identify the titration: Weak base ($\mathrm{NH_4OH}$) in flask, strong acid (HCl) added from burette.

Step 2 — Expected pH curve:

• Initially: $\mathrm{NH_4OH}$ solution $\rightarrow$ pH ≈ 11 (basic)
• As HCl is added: Buffer region forms ($\mathrm{NH_4OH/NH_4Cl}$) $\rightarrow$ pH decreases gradually
• At half-equivalence point: pH = pOH = pKb = 4.74, so pH = 9.26
• At equivalence point: Only $\mathrm{NH_4Cl} \rightarrow$ pH ≈ 5 (acidic, sharp drop)
• After equivalence: Excess HCl $\rightarrow$ pH drops to ≈ 1-2

Step 3: The correct graph starts at high pH (~11), decreases with a buffer region, has a sharp drop at equivalence point (but less sharp than strong acid/strong base), and ends at low pH.

Answer: Option (1)