What elements contains a full third energy level and what element contains the first p electron??

Here is an interactive site that will show you how the 1s, 2s, 2p, etc levels fill. Post your answers here if you want someone to check them. Also, you need to clarify what you mean by a third energy level if you repost. Is that the d electron level or the n=3 level? Anyway, your answers are on the site below.
http://www.iun.edu/~cpanhd/C101webnotes/modern-atomic-theory/aufbau-principle.html

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To determine the elements that contain a full third energy level, we need to consider the electron configuration of elements up to the third energy level.

According to the Aufbau principle, electrons fill orbitals in a specific order. The first energy level (n=1) contains only one orbital, called the 1s orbital, which can hold a maximum of two electrons. The second energy level (n=2) contains four orbitals: 2s and three 2p orbitals. The 2s orbital can hold two electrons, while each of the 2p orbitals can hold two electrons as well, resulting in a total of eight electrons in the second energy level.

Moving on to the third energy level (n=3), it can hold a total of 18 electrons. The 3s orbital can hold two electrons, and the three 3p orbitals can also hold two electrons each, giving us a total of six electrons so far. The remaining ten electrons fill the five 3d orbitals, with each orbital accommodating two electrons.

Therefore, the elements that contain a full third energy level are those with the electron configuration [Ar] 3s² 3p⁶ 3d¹⁰.

Regarding the element that contains the first p electron, we need to look at the order in which orbitals are filled. Since the first energy level (n=1) does not have a p orbital, we move on to the second energy level (n=2). Within the second energy level, the 2p orbital is the first to be filled. Therefore, the element that contains the first p electron is the one with the electron configuration 2p¹.