Question

The electron first occupies the following orbital according to the Aufbau principle

• A. 5s
• B. 4p
• C. 3d
• D. 5p

Hint:

Remember the Aufbau filling order: \[ 1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d \rightarrow 4p \rightarrow 5s. \] The \(4s\) orbital is filled before the \(3d\) orbital.

Answer 1

The Correct Option is C

Concept: According to the Aufbau principle, electrons occupy orbitals in the order of increasing energy. The filling order is \[ \boxed{ 1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p\cdots } \]

Step 1: Compare the given orbitals.
Among the given options, \[ 3d,\;4p,\;5s,\;5p, \] the orbital with the lowest energy is \[ \boxed{3d.} \] Hence, it is occupied first.

Step 2: Final conclusion.
Therefore, according to the Aufbau principle, the electron first occupies \[ \boxed{3d.} \]