Question

how many electrons occupy... a filled 3rd energy level a filled 7s sublevel any f sublevel the 4p sublevel of a neutral atom of bromine

Explanation:

Step1: Recall electron - capacity formula for energy level

The number of electrons in an energy level $n$ is given by $2n^{2}$. For $n = 3$, we calculate $2\times3^{2}=2\times9 = 18$.

Step2: Recall electron - capacity of s - sublevel

The s - sublevel has 1 orbital, and each orbital can hold 2 electrons. So a filled s - sublevel (like 7s) has 2 electrons.

Step3: Recall electron - capacity of f - sublevel

The f - sublevel has 7 orbitals. Since each orbital can hold 2 electrons, a filled f - sublevel has $2\times7=14$ electrons.

Step4: Recall electron - configuration of Bromine

The atomic number of Bromine (Br) is 35. Its electron - configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{5}$. The 4p sublevel of Bromine has 5 electrons.

Answer:

18
2
14
5