Question

question 2 of 10
which of the following elements has 2 electrons in the 4s sublevel?

a. mg
b. ca
c. k
d. ar

Explanation:

To determine which element has 2 electrons in the 4s sublevel, we analyze the electron configurations of each option:

• Option A (Mg): Magnesium has an atomic number of 12. Its electron configuration is $1s^2 2s^2 2p^6 3s^2$. The outermost electrons are in the 3s sublevel, not the 4s.
• Option B (Ca): Calcium has an atomic number of 20. Its electron configuration is $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$. Here, the 4s sublevel contains 2 electrons.
• Option C (K): Potassium has an atomic number of 19. Its electron configuration is $1s^2 2s^2 2p^6 3s^2 3p^6 4s^1$. The 4s sublevel has 1 electron, not 2.
• Option D (Ar): Argon has an atomic number of 18. Its electron configuration is $1s^2 2s^2 2p^6 3s^2 3p^6$. There are no electrons in the 4s sublevel as it is a noble gas with a filled valence shell in the 3rd energy level.

Answer:

B. Ca