A statement of Assertion followed by a statement of Reason is given. Choose the correct answer out of the following options. Assertion : Energy of 2 ~s orbital of Hydrogen is less than the energy of the 2 ~s orbital of Lithium. Reason : Energies of orbitals in the same subshell decrease with increase in atomic number.

Step-by-step solution

For a hydrogen-like atom or ion, the energy of an orbital with principal quantum number n is given by E_n = -13.6 Z^2 n^2 eV, where Z is the atomic number. For the 2s orbital of Hydrogen ( Z=1 ), E_ H, 2s = -13.6 1^2 2^2 = -3.4 eV. For the 2s orbital of Lithium ( Z=3 ), E_ Li, 2s = -13.6 3^2 2^2 = -13.6 2.25 = -30.6 eV. Comparing the values, -30.6 eV is less than -3.4 eV, meaning the energy of the 2s orbital of Lithium is lower than that of Hydrogen. Thus, the Assertion is incorrect. The Reason states that energies