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 $\to$ lead nitrate
If Gelatinous white $\mathrm{ppt}\to$ zinc nitrate
On adding excess ${\mathrm{NH}}_4\mathrm{OH}$
Chalky white ppt remains insoluble confirming the presence of lead nitrate
Gelatinous white ppt dissolves confirming the presence of zinc nitrate.