Solution. The atomic number of phosphorus is 15. Thus, a phosphorus atom contains 15 electrons. The order of filling of the energy levels is 1 s, 2 s, 2 p, 3 s, 3 p, 4 s, . . . The 15 electrons of the phosphorus atom will fill up to the 3 p orbital, which will contain three electrons: The last electron added is a 3 p electron.. An electron has spin quantum number (s) +1/2 and magnetic quantum number is -1. It can be present in: This question has multiple correct options A s− orbital B d− orbital C p− orbital D f− orbital Medium Solution Verified by Toppr Correct options are B) , C) and D) For a particular l value there should be m values from −m to +m. It has been found that the magnitude of the intrinsic spin angular momentum S of an electron is given by. S = s ( s + 1) ℏ, 8.26. where s is defined to be the spin quantum number. This is similar to the quantization of L given in Equation 8.4, except that the only value allowed for s for an electron is s = 1 / 2..