Question

the atom of an element is made up of 4 protons, 5 neutrons and 4electrons. Write down its atomic number and its mass number​

Answer 1

Answer:

So, for beryllium, there are 4 protons, 5 neutrons and 4 electrons but to calculate atomic mass number, four electrons won't be counted. Hence the atomic mass number of beryllium will be the sum of 4 protons and 5 neutrons and that will be equal to 9.