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As an electron makes a transition from an excited state to the ground state of a hydrogen - like atom/ion:

1. kinetic energy decreases, potential energy increases but total energy remains same
2. kinetic energy and total energy decrease but potential energy increases
3. its kinetic energy increases but potential energy and total energy decrease
4. kinetic energy, potential energy and total energy decrease

Correct answer: its kinetic energy increases but potential energy and total energy decrease

Solution

As the electron transitions to a lower energy state, it moves closer to the nucleus, which increases its kinetic energy due to the attractive force. However, the potential energy decreases because it is at a lower energy level, resulting in a decrease in total energy.

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