The given figure shows a pie chart of the constituent gases in the atmosphere:

The portion of the pie chart representing oxygen is:

Radha wakes up in the morning and observes a beam of sunlight entering her room from a tiny hole in the window. She sees some tiny shining particles which appear to dance merrily around in the air.

The particles shows that air contains:

Which catalyst is used in the following reaction:

$2{\mathrm{H}}_2{\mathrm{O}}_2\to 2{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2$