Question: how to find how many unpaired electrons?
Answer: For example, the element P, has an atomic mass of 15. So the electron configuration is 1s^2, 2s^2, 2p^6, 3s^2, 3p^3 (The exponents add up tp 15). Once you figure out the electron configuration, you fill up the corresponding orbitals with electrons, any left with one is considered unpaired.