Here's why:

* Principal Quantum Number (n): The principal quantum number determines the energy level of an electron.

* Orbital Types: Each energy level can hold different types of orbitals:

* n=1: Only the 1s orbital

* n=2: 2s and 2p orbitals

* n=3: 3s, 3p, and 3d orbitals

* n=4: 4s, 4p, 4d, and 4f orbitals

So, the 3d orbitals are first found in the third energy level (n=3).