Step 1: Thermal decomposition.
\( 2KMnO_4 \xrightarrow{513\text{K}} K_2MnO_4 + MnO_2 + O_2 \).
Step 2: K2MnO4 properties.
Potassium manganate: dark green, Mn = +6, one unpaired electron, paramagnetic.
Step 3: Final.
\[ \boxed{K_2MnO_4 \text{ - green, paramagnetic}} \]