Questions

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.

A Jigsaw puzzle.

Africa - 54 countries

South America - 12 countries

Antarctica - 0 countries

Europe - 43 countries.

Hence, Antarctica continent has the least countries.

Paper production is basically a two-step process in which a fibrous raw material is first converted into pulp, and then the pulp is converted into paper. The harvestedwood is first processed so that the fibres are separated from the unusable fraction of the wood, the lignin. Pulp making can be done mechanically or chemically. In the chemical pulping process, alkali (e.g., sodium hydroxide in the form of a lye or caustic soda) is usually used to remove the lignin that binds the fibres. So, for degumming of raw material, caustic soda is used.