<p><strong>Noun</strong></p><ul><li>Chemistry</li><li>a hard, brittle, grayish-white, metallic element</li><li>an oxide of which (MnO₂) manganese dioxide is a valuable oxidizing agent</li><li>used chiefly as an alloying agent in steel to give it toughness</li><li>Mn</li><li>54.938</li><li>25</li><li>7.2 at 20°C</li></ul>