The energy of second Bohr orbit of the hydrogen atom is -328 kJ mol-1 ; hence the energy of fourth Bohr orbit would be :

According to the Bohr model, the energy of the nth orbit of a hydrogen atom is given by the formula En = -13.6 eV / n^2. Given that the energy of the second Bohr orbit is -328 kJ/mol, we first need to convert this energy into electronvolts (eV) per atom to apply the formula directly, knowing that 1 eV = 96.485 kJ/mol. The energy in eV for the second orbit is -328 kJ/mol / 96.485 kJ/mol/eV = -3.4 eV. However, using the formula directly with n=2 should give us the energy in eV, and then we can calculate the energy for n=4. The energy for the second orbit (n=2) is En = -13.6 / 2^2 = -3.4 eV, which matches the given energy when converted. For the fourth orbit (n=4), the energy would be E4 = -13.6 / 4^2 = -0.85 eV. To convert this back into kJ/mol, we multiply by 96.485 kJ/mol/eV, giving us -0.85 eV * 96.485 kJ/mol/eV = -82 kJ/mol. Therefore, the energy of the fourth Bohr orbit would be -82 kJ/mol. So, the correct answer is option (D) -82 kJ mol-l. Think of it this way: the energy of the orbits in the Bohr model decreases as the orbit number increases, and we can use the formula to calculate the energy of any given orbit.