Correct Option (B)

The person is initially positioned on the 1st step of the ladder. To reach the middle step, the person climbs 4 additional steps. Therefore, the middle step is located at step number 1 + 4 = 5.

For a ladder with N steps, the middle step is given by the formula $\frac{N + 1}{2}$ , assuming N is an odd number to ensure a unique middle step. Equating the calculated middle step position with the formula:

5 = \frac{N + 1}{2}

Multiplying both sides by 2:

10 = N + 1

Subtracting 1 from both sides:

N = 9

Thus, the ladder has 9 steps.

Incorrect Options:

If the ladder has 8 steps (Option A) or 10 steps (Option C), it contains an even number of steps. A ladder with an even number of steps does not possess a unique middle step, which contradicts the premise of the question implying a singular "middle step."

If the ladder has 11 steps (Option D), the middle step would be $\frac{11 + 1}{2} = 6$ th step. However, according to the problem, the person reaches the 5th step (1st step + 4 more steps) to arrive at the middle step. This contradicts the calculation for an 11-step ladder, where the middle step is the 6th step.