Question

question 1 (2 points)
the electron configuration of the element whose atomic number is 25 is:
1s²2s²2p⁶3s²3p⁶3d⁵4s²
1s²2s²2p⁶3s²3p⁶4s²3d⁴4p¹
1s²2s²2p⁶3s²3p⁶4s⁰3d⁷
1s²2s²2p⁶3s²3p⁶4s²3d⁵

Explanation:

Step1: Determine the element

The element with atomic number 25 is manganese (Mn).

Step2: Apply Aufbau principle

According to the Aufbau principle, electrons fill orbitals in the order of increasing energy: \(1s < 2s < 2p < 3s < 3p < 4s < 3d\).

Step3: Fill electrons

• \(1s\) can hold 2 electrons: \(1s^{2}\)
• \(2s\) can hold 2 electrons: \(2s^{2}\)
• \(2p\) can hold 6 electrons: \(2p^{6}\)
• \(3s\) can hold 2 electrons: \(3s^{2}\)
• \(3p\) can hold 6 electrons: \(3p^{6}\)
• \(4s\) is filled before \(3d\) (lower energy), \(4s\) can hold 2 electrons: \(4s^{2}\)
• Then \(3d\) orbitals start filling. Manganese has 25 electrons. After filling \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}\) (total \(2 + 2+6 + 2+6 + 2=20\) electrons), there are \(25 - 20 = 5\) electrons left for \(3d\) orbitals: \(3d^{5}\)

Answer:

\(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{5}\) (the fourth option)