Lead nitrate and Zinc nitrate solutions can be distinguished by adding Ammonium hydroxide solution till in exess.On adding few drops of $\mathrm{NH}_4\mathrm{OH}$If Chalky white ppt $\rightarrow$ lead nitrateIf Gelatinous white $\text{ppt} \rightarrow$ zinc nitrateOn adding excess $\mathrm{NH}_4\mathrm{OH}$Chalky white ppt remains insoluble confirming the presence of lead nitrateGelatinous white ppt dissolves confirming the presence of zinc nitrate.