Explanation:

- Pyrolusite is an ore of manganese.

- Pyrolusite is primarily composed of manganese dioxide (MnO2).

- It is one of the most important manganese ores used in the production of various manganese compounds and alloys.

- Option:2, chromium

- The principal ore for chromium is chromite, not pyrolusite.

- Option:3, titanium

- Titanium is often extracted from ores such as rutile and ilmenite.

- Option:4, uranium

- Uranium is mainly extracted from ores like pitchblende and uraninite.

- Correct Answer: Option:1, manganese