Step 1: Understand oxidation states and oxide nature
Oxides of elements, particularly transition metals like manganese, can exhibit varying acid-base properties depending on the oxidation state:
- Lower oxidation states ⇒ Basic or amphoteric oxides
- Higher oxidation states ⇒ More acidic oxides
Step 2: Assign oxidation states to given compounds
- MnO: Mn is in +2 oxidation state ⇒ basic oxide
- Mn2O3: Mn is in +3 oxidation state ⇒ weakly basic/amphoteric
- MnO2: Mn is in +4 oxidation state ⇒ amphoteric
- Mn2O7: Mn is in +7 oxidation state ⇒ strongly acidic
Step 3: Conclusion
Mn
2O
7 has the highest oxidation state of +7 for manganese. Hence, it is the most acidic oxide among the options given.
\[
\boxed{\text{Mn}_2\text{O}_7 \text{ is the most acidic oxide}}
\]