Question

an atom has the electron configuration of 1s²2s²2p⁵. how many electrons are in that atom?
a eight
b nine
c ten
d six

Explanation:

Step1: Identify electron - count in each sub - shell

The superscripts in the electron configuration represent the number of electrons in each sub - shell. For $1s^{2}$, there are 2 electrons in the 1s sub - shell. For $2s^{2}$, there are 2 electrons in the 2s sub - shell. For $2p^{5}$, there are 5 electrons in the 2p sub - shell.

Step2: Calculate total number of electrons

Add the number of electrons in each sub - shell: $2 + 2+5=9$.

Answer:

B. Nine