Questions

A Jigsaw puzzle.

New York City, London, and Tokyo are the richest cities in the world 2018, according to their ranks.

In chemistry rusting is called as oxidation. Oxidation is a chemical process where metal gains oxygen and become oxide. In rusting the Iron ore make a chemical reaction with the oxygen in the presence of water and environmental or atmospheric moisture to produce an Iron oxide. Iron oxide is otherwise called as rust.

The rusting of iron is a chemical change because it is two substances reacting together to make a new substance. 

Rusting would only be a physical change if iron molecules remained pure iron throughout the process.

The organs protected by the thoracic cage include the lungs and the heart.

Africa - 54 countries

South America - 12 countries

Antarctica - 0 countries

Europe - 43 countries.

Hence, Antarctica continent has the least countries.