Yellow compound of lead chromate gets dissolved on treatment with hot NaOH solution. The product of lead…

Lead chromate is yellow in color due to their absorption and reflection of specific wavelengths of light.

${\mathrm{PbCrO}}_4 + \mathrm{NaOH} (\mathrm{hot} \mathrm{excess}) \to \left[\mathrm{Pb}\right(\mathrm{OH}{)}_4]{ }^{-2} + {\mathrm{Na}}_2{\mathrm{CrO}}_4$

The complex formed is ${\left[\mathrm{Pb}{\left(\mathrm{OH}\right)}_4\right]}^{2-}$

which has coordination number $=4$ and complex is dianionic due to presence of $\left(-2\right)$ charge.

coordination number, the number of atoms, ions, or molecules that a central atom or ion holds as its nearest neighbours in a complex or coordination compound or in a crystal.