Indicate the number of electrons at the external energy level of atoms: a) phosphorus b) calcium c) boron

From the periodic table of chemical elements, we can learn basic information about the structure of atoms:
– the charge of the nucleus, the number of protons and electrons is equal to the ordinal number of the element;
– the difference between the atomic mass and the serial number shows the number of neutrons in the nucleus of an atom;
– the number of energy levels is the number of the period;
– THE NUMBER OF ELECTRONS AT THE EXTERNAL ENERGY LEVEL is equal to the GROUP NUMBER.
Means:
phosphorus (P, 5group) – 5e; calcium (Ca, group 2) – 2e, boron (B, group 3) – 3e.