Concept: Historically and practically, the Balmer series transitions (falling to the \( p=2 \) level) fall directly into a specific, biologically and technologically relevant slice of the electromagnetic spectrum.

Formula:
$$ \lambda_{\text{Balmer}} \in [400 \text{ nm}, 700 \text{ nm}] $$

Solution:

• The Balmer series represents transitions where photons possess energies between ~1.9 eV and 3.4 eV.
• These specific energy photons correspond to wavelengths between approximately 400 nm and 700 nm.
• This specific band is the "Visible Region" of the spectrum, making the Balmer series easily observable to the human eye, which is why it was historically the first series to be discovered and modeled.

Why other options are incorrect:
Quantum theory (A) applies universally to all series. Hydrogen exhibits many series (C is wrong). The lowest possible quantum number \( n \) (D) defines the Lyman series (ground state, \( n=1 \)), not Balmer.