Final answer:
Option 1: 3f is not a possible electron configuration, as f subshells are not available in the third energy level; they begin at the fourth level (n=4).
Step-by-step explanation:
The answer to the question of which of the following is not possible: 3f, 2s, 2p, 5p 4d, is Option 1: 3f. The electron configuration notation of 3f is not allowed because there are no f subshells in the third energy level; f subshells start from the fourth energy level (n=4). The notation violates the rules of quantum mechanics regarding electron configurations. The 2s and 2p notations are allowed for the second energy level, and while 5p is a valid notation for the fifth energy level, 4d is also allowed as d subshells start from the third energy level. Overall, the configuration that is not possible according to the principles of atomic structure is 3f.