Question

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1. what is the electron configuration of beryllium?

Explanation:

Step1: Find beryllium's atomic number

Beryllium (Be) has atomic number 4, so 4 electrons.

Step2: Fill orbitals by Aufbau principle

1s orbital holds max 2 electrons first: $1s^2$. Remaining 2 electrons go to 2s: $2s^2$.

Step3: Combine orbitals

Electron configuration is $1s^22s^2$.

Answer:

$1s^22s^2$