Identify the confirmatory tests for $\mathrm{Pb}^{2+}$

In salt analysis, $\mathrm{Pb}^{2+}$ is commonly confirmed by formation of characteristic insoluble salts:

• With chromate ions: $\mathrm{Pb}^{2+} + \mathrm{CrO_4}^{2-} \rightarrow \mathrm{PbCrO_4}(s)$ This gives yellow lead chromate.

• With iodide ions: $\mathrm{Pb}^{2+} + 2\mathrm{I}^- \rightarrow \mathrm{PbI_2}(s)$ This gives yellow lead iodide.

• With sulphate ions: $\mathrm{Pb}^{2+} + \mathrm{SO_4}^{2-} \rightarrow \mathrm{PbSO_4}(s)$ This gives white lead sulphate.

Check lead nitrate

Lead nitrate is: $\mathrm{Pb(NO_3)_2}$

But nitrate salts are generally soluble, and formation of lead nitrate is not used as a confirmatory test for $\mathrm{Pb}^{2+}$ in qualitative analysis.

Evaluate options

• A: lead chromate → confirmatory test
• B: lead iodide → confirmatory test
• C: lead sulphate → confirmatory test
• D: lead nitrate → not a confirmatory test

Conclusion

The compound whose formation is not a confirmatory test for $\mathrm{Pb}^{2+}$ is: $\boxed{\mathrm{Pb(NO_3)_2}}$ i.e. Option D.