Question

An electron makes a transition from an excited state to the ground state of a hydrogen like atom. Out of the following statements which one is correct ?
(A) K.E, P. E. and T.E. decreases
(B) K.E. increases but P. E. and T.E. decreases
(C) K.E. and T.E. decreases but P.E. increases
(D) K.E. decreases, P.E. increases but T.E. remains the same

• A. A
• B. B
• C. C
• D. D

Hint:

In a Bohr orbit KE is the negative of total energy and PE is twice the total energy.

Answer 1

The Correct Option is B

Step 1: Orbit radius
A lower orbit has a smaller radius. The electron is closer to the nucleus, so the attraction is stronger and the PE is more negative.

Step 2: Speed
A smaller orbit means a higher speed, as $v\propto\frac Zn$. So KE rises. Total energy $= K+U = -K$ falls. Statement (B).

Final Answer:
Statement B. \[ \boxed{\text{(B)}\ \text{KE increases, PE and TE decrease}} \]