Select the correct characteristic about ${\mathrm{Mn}}_2{\mathrm{O}}_7$

Ionic character reduces as a metal's oxidation number rises. ${\mathrm{Mn}}_2{\mathrm{O}}_7$, which is a covalent green oil, is the case for $\mathrm{Mn}$.

The inorganic substance having the formula ${\mathrm{HMnO}}_4$ is known as permanganic acid (also known as manganic(VII) acid). As its dihydrate, this potent oxoacid has been isolated.

A base has a greater pH than acidic substances, which have a lower $\mathrm{pH}$. Vinegar and various other acids are both acidic.

Hence, the correct option is D.