When a large amount of ${\mathrm{KMnO}}_4$ is added to concentrated ${\mathrm{H}}_2{\mathrm{SO}}_4$, an explosive compound is formed. The formula of the compound is

${\mathrm{KMnO}}_4$ is pink color compound and itself is very explosive, when it reacts with acid sulphuric acid then it forms a highly explosive compound because the high amount of energy is required to break and form a bond, therefore, this energy is stored in the newly formed bond.

Hence, the formula of the formed compound is ${\mathrm{Mn}}_2{\mathrm{O}}_7$