1. why do all atoms of an element have the same atomic number, although they may have different mass numbers?
2. what do we call atoms of the same element with different mass numbers?
3. explain the meaning of each term in the symbol
(az)x

Atoms of an element have the same atomic number but different mass numbers because the atomic number only contains the amount of protons in an element.
Atoms of the same element that have different mass numbers are called isotopes.
With (AZ)X, the A is the number of protons, the Z is the number of neutrons, and the X is the electrons.

Standing in the sunlight and feeling the heat on your face (uv radiation is entering the skin, converting to infrared radiation, and is absorbed by your tissues)orstanding near a fire and feeling the heat on your skin (infrared radiation transfer)