The number following the symbol represents a change in

he number following the symbol represents a change in neutrons and mass numbers.

Explanation:

The chemical symbol is the abbreviation used to identify the element or atom of the element. The isotope symbols of specific element is recorded by placing a mass number as superscript in left to the element's symbol. The protons count (also referred as atomic number) as subscript precedes the symbol. For example, magnesium is the three isotopes mixture with 12 as atomic number and a mass numbers as 24, 25 and 26.

These isotopes can identify as . These isotope symbols are read as "element, mass number" and can be symbolized by this reading. For example, is read as "Magnesium 24" and so on. All magnesium atoms contain 12 protons in the nucleus. So, it indicates the neutron variation and mass numbers.

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me