Answer:
b) n = 1 to n = 4.
Explanation:
a ) n = 4 to n = 1 transition represents release of energy because transition is from high energy orbit to low energy orbit.
Similarly c) n = 2 to n = 1 represents release of energy because transition is from high energy to low energy orbit.
d ) n = 1 to n = 3 is also energy absorbing transition but amount of energy absorbed is less as compared with option b) transition .
So the correct option is b)