Read the following statements regarding energy levels, and identify the correct statements.

(A) The energy of an atom is least when its electron is revolving in an orbit closest to the nucleus
(B) the energy levels of the excited states come closer and closer together as principal quantum number increases
(C) ionisation energy of the hydrogen atom is the minimum energy required to free the electron from the ground state of the hydrogen atom
(D) as the excitation of hydrogen atom increases, the value of minimum energy required to free the electron from the excited atom decreases.

Choose the correct answer from the options given below:

(A), (B), (C) and (D)

The correct answer is Option (3) → (A), (B), (C) and (D)

(A) Correct → Lowest energy (ground state) is when the electron is in the orbit closest to the nucleus.

(B) Correct → Energy levels converge as $n \to \infty$.

(C) Correct → Ionisation energy of H is energy required to remove electron from ground state.

(D) Correct → If electron is already in an excited state, less energy is required for ionisation.

Final Answer: (A), (B), (C), (D) are all correct.