Monazite is an ore of:(A) Titanium(B) Thorium(C) Zirconium(D) Iron

Monazite is an ore of Thorium.

Explanation:
Monazite is a phosphate mineral that contains a variety of rare earth elements, most notably thorium, lanthanum, and cerium. It is considered a significant source of thorium, a radioactive element used in nuclear reactors. It also contains small amounts of uranium. Among the given options:

Titanium: Found in ores like ilmenite and rutile.
Thorium: Found in monazite.
Zirconium: Found in ores like zircon.
Iron: Found in ores like hematite and magnetite.
Hence, the correct answer is (B) Thorium.