Q1: Monazite deposits constitute an important source for the following metal.

ANS:A - Thorium

Thorium is a naturally occurring radioactive metal with the chemical symbol Th and atomic number 90. Here's an explanation of thorium:

1. Occurrence: Thorium is found in various minerals and ores, with monazite and thorite being the most common sources. Monazite sand, a rare earth phosphate mineral, is one of the primary sources of thorium, often containing significant thorium content alongside other rare earth elements.
2. Properties: Thorium is a silvery-white metal that is soft, ductile, and malleable when pure. It is relatively stable in air and water but tarnishes slowly. Thorium is weakly radioactive, emitting alpha particles, and has a long half-life of over 14 billion years.
3. Applications:
   • Nuclear Energy: Thorium is primarily known for its potential as a nuclear fuel in thorium-based nuclear reactors. While thorium itself is not fissile, it can be transmuted into fissile uranium-233 through neutron irradiation. Thorium-based nuclear reactors offer several potential advantages over conventional uranium-based reactors, including reduced nuclear waste, increased safety, and enhanced proliferation resistance.
   • Alloys: Thorium is used as an alloying element in various metals, such as magnesium and aluminum, to improve their mechanical properties and high-temperature performance.
   • Lighting: Thorium oxide (ThO2) is used in gas mantles for lanterns and lamps to produce a bright white light when heated.
4. Health and Safety: While thorium itself is not highly radioactive compared to some other radioactive elements, its decay products, including radon gas and radium, can pose health risks if proper precautions are not taken during handling and processing.
5. Regulation: Due to its radioactivity and potential nuclear applications, thorium is subject to regulation in many countries. The mining, processing, and use of thorium are often governed by strict regulations to ensure safety and environmental protection.

In summary, thorium is a naturally occurring radioactive metal with various applications, including its potential as a nuclear fuel, alloying element, and lighting component. Despite its radioactivity, thorium offers several advantages and continues to be of interest in nuclear energy research and development.