Does this picture show a physical or chemical change?

Asingle atom of an element has 21 neutrons, 20 electrons, and 20 protons. which element is it? ok o z

Acm ruler with main graduations from 1 to 10 from left to right there are 10 secondary graduations between each of the main graduations there is a line that begins. at the left end of the ruler 10 secondary graduations to the left of the “1 main graduation the right end of the line ends on the eighth secondary graduation to the right of 3 how long is the line

How many peaks will be present in a mass spectrum for brcl?