The ionisation energy of hydrogen is the energy needed to move the electron from

  • A. n equals 1 to n equals 2
  • B. n equals 2 to n equals 1
  • C. n equals 1 to infinity
  • D. infinity to n equals 1

Explanation

Ionisation means removing the electron completely, so it must be raised from the ground state to the level where its energy is zero, which is n at infinity, and that requires 13.6 eV. Moving between two bound levels needs less energy and simply excites the atom. The energy released in the reverse process is emitted as a photon.

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