Questions

Alum is a common alum, potassium aluminum sulphate K2SO4.Al2SO43.24H2O which makes colloidally suspended impurities in water such as clay to settle down.

A restrictive clause is one that limits the meaning of the word it describes.

For example :: 

The girl who lives next door is beautiful.

This restrictive clause limits "the girl" to say it's specifically the one next door.

Yes, a promise can be broken without being held.

Cosmology is the scientific study of the large scale properties of the universe as a whole. It endeavors to use the scientific method to understand the origin, evolution and ultimate fate of the entire Universe.

Depending on the outcome of the observations, the theories will need to be abandoned, revised or extended to accommodate the data. The prevailing theory about the origin and evolution of our Universe is the so-called Big Bang theory.