Which of these elements has an electron configuration of [tex]$[ Kr ] 5s^2$[/tex]?

A. Barium
B. Calcium
C. Rubidium
D. Strontium



Answer :

To determine which element has the electron configuration of [tex]\([ \text{Kr} ] \, 5s^2\)[/tex], let's break down the information given:

1. We're looking for an element that follows the noble gas krypton ([tex]\([\text{Kr}]\)[/tex]).
2. The configuration also specifies [tex]\(5s^2\)[/tex], indicating there are two electrons in the 5th shell's s orbital.

Now, let's review the electron configurations of the given options:

1. Barium (Ba):
- Atomic number: 56
- Electron configuration: [tex]\([ \text{Xe} ]\, 6s^2\)[/tex]

2. Calcium (Ca):
- Atomic number: 20
- Electron configuration: [tex]\([ \text{Ar} ]\, 4s^2\)[/tex]

3. Rubidium (Rb):
- Atomic number: 37
- Electron configuration: [tex]\([ \text{Kr} ]\, 5s^1\)[/tex]

4. Strontium (Sr):
- Atomic number: 38
- Electron configuration: [tex]\([ \text{Kr} ]\, 5s^2\)[/tex]

From the configurations above, Strontium (Sr) is the element that has the electron configuration [tex]\([ \text{Kr} ]\, 5s^2\)[/tex].

Thus, the element with the electron configuration [tex]\([ \text{Kr} ] \, 5s^2\)[/tex] is strontium.