Consider the given acid ionization constants. identify the strongest conjugate base. acid ka hno2(aq) 4.6×10−4 hcho2(aq) 1.8×10−4 hclo(aq) 2.9×10−8 hcn(aq) 4.9×10−10 part a no−2(aq) cho−2(aq) cn−(aq) clo−(aq)

The higher value of Ka indicates the higher acid strength and also the stronger the acid the weaker its conjugate base and vice versa.
So here we looking for the weakest acid which has lowest Ka value because it will has the strongest conjugate base:
This acid is HCN due to it has the smaller value of Ka 4.9 x 10⁻¹⁰ and the strongest base will be CN⁻(aq)

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