Q1. A yellow monoxide that dissolves in hot and conc. alkali.

The correct option is C

Lead Oxide

• Lead Oxide is the yellow monoxide which dissolves in hot and conc. alkali solution.
• The reaction of Lead oxide with hot and conc. alkali $\mathrm{NaOH}$ is:

$\underset{\mathrm{Lead}\mathrm{oxide}}{{\mathrm{PbO}}_2}+\underset{\mathrm{Sodium}\mathrm{hydroxide}}{\mathrm{NaOH}}\to \underset{\mathrm{Sodium}\mathrm{hexahydroxoplumbate}}{{\mathrm{Na}}_2\left[{\mathrm{PbO}}_2\right]}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}}$

Thus option C is the correct choice.