How many electrons does it need to complete it's outer energy level in a phosphorous atom

It needs 5 electrons. I would start by looking at a periodic table. The numbers on top are group numbers. Below each number is roman symbols like (lA, llA, IIIB, etc.). Phosphorus is in group 15. Under fifteen it has the Roman numeral of 5 (VA). There is a pattern in the periodic table. Each Roman numeral stands for how many valence electrons it has. Valence electrons are the outermost electrons of an atom.

True to the fact it is actually false