Question

In which transition, one quantum of energy is emitted?
(A) ${\text{n = 4 }} \to {\text{ n = 2}}$
(B) ${\text{n = 3 }} \to {\text{ n = 1}}$
(C) ${\text{n = 4 }} \to {\text{ n = 1}}$
(D) ${\text{n = 2 }} \to {\text{ n = 1}}$

Answer 1

Hint: Electrons in an atom tend to switch from one orbital to another. When an electron jumps from lower energy level to higher energy level, it needs energy which it absorbs from the surrounding and when it jumps from higher energy level to lower energy it releases some amount of energy.

Complete step by step solution:
We know that the electrons revolve around the nucleus in specific orbits. These orbits are called stationary orbits or energy levels. They are generally numbered from n=1, 2, 3, 4….and so on. These numbers are known as principal quantum numbers. Each orbit is assigned a specific number and has a certain amount of energy.
Whenever an electron jumps from a lower energy level to higher, it needs some amount of energy which it absorbs from the surrounding. The electron makes transition only when it has sufficient energy to reach the next orbital.
On the other hand, when an electron jumps from a higher energy level to lower one, it releases energy in the form of radiations. It will make a transition only when its energy is reduced sufficiently.
In all of the options given above, electrons moved from a higher energy level to a lower one. So, a quantum of energy is emitted in all the above-mentioned transitions.
Hence, all of the options are correct.

Additional information:
Energy of a particular orbital is given by the formula ${{\text{E}}_{\text{n}}}{\text{ = - }}{{\text{R}}_{\text{h}}}\dfrac{1}{{{{\text{n}}^2}}}$. Where ${{\text{R}}_{\text{h}}}$is Rydberg’s constant and has numerical value ${\text{2}}{\text{.18 }} \times {\text{1}}{{\text{0}}^{ - 18}}{\text{ J}}$.

Note: Remember that transition from a lower to higher energy level requires absorption of energy and transition from higher to lower level results in release of excess energy.