In conductometric titration of HCl (strong acid) and CH₃COOH (weak acid) with NH₄OH (weak base), the conductivity changes in three distinct stages. First, H⁺ from HCl is neutralized, forming NH₄⁺Cl^-, causing a sharp decrease in conductivity due to replacement of high mobility H⁺ with lower mobility NH₄⁺. Second, H⁺ from CH₃₃COO^-NH₄⁺; the weak dissociation of CH₃COOH means conductivity decreases slowly. Finally, after both equivalence points, excess NH₄OH adds, slightly increasing conductivity as NH₄⁺ and OH^- ions accumulate. The graph shows two descending lines with different slopes, the first steeper than the second, followed by a slight upward curve.

Final Answer: The first graph (top-left image) is correct.