Which electronic level allows the hydrogen atom to absorb a proton but not to emit a photon?

\(1s\)

The correct answer is option 3. \(1s\).

When a hydrogen atom absorbs a proton, it undergoes a process called ionization, where the electron in the hydrogen atom is removed. This occurs because the proton has a positive charge, and when it encounters the hydrogen atom, it can attract and bind with the electron, effectively removing it from the hydrogen atom.

The electronic level that allows the hydrogen atom to absorb a proton but not emit a photon is the 1s orbital. In the ground state of a hydrogen atom, the electron is typically found in the 1s orbital, which is the lowest energy level orbital.

When the hydrogen atom absorbs a proton, the energy required for this process is typically greater than the energy difference between the 1s orbital and any higher energy level orbitals. As a result, the absorbed energy is used to remove the electron from the 1s orbital, leading to ionization of the hydrogen atom.

Since the absorbed energy is used to remove the electron, no excess energy is available for the emission of a photon. Therefore, when a hydrogen atom absorbs a proton at the 1s electronic level, it does not emit a photon. Instead, the absorbed energy is used to ionize the hydrogen atom.