Atoms of the same element with varying number of neutrons are called

Isotopes

The number of neutrons can vary, but not protons. This is called an isotope. An example is deuterium, an isotope of hydrogen with an extra neutron, but the same number of protons.

blue light is scattered in different directions by the tiny molecules of air. blue is scattered more than other colours because it has a shorter distance to travel which results in smaller waves. this is why we see a blue sky most of the time.