Seven persons — A, B, C, D, E, F and G — are attending an event one after another, but not necessarily in the same order. G attends the event three persons after C. B attends the event immediately before C. Only one person attends the event between B and E. D attends the event four persons after E but before A. Three persons attend event between A and F.

If all the persons are arranged in alphabetical order in the sequence from first to the last person to attend the event, then position of how many persons remains unchanged?

The correct option is One.

Step-by-Step Breakdown:

1. Analyze the given clues:

• "G attends the event three persons after C" means there are 2 persons between C and G ($\text{C},\text{\_},\text{\_},\text{G}$).

• "B attends the event immediately before C" gives the sequence: $\text{B},\text{C},\text{\_},\text{\_},\text{G}$.

• "Only one person attends the event between B and E" places E two positions before B, forming: $\text{E},\text{\_},\text{B},\text{C},\text{\_},\text{\_},\text{G}$.

• "D attends the event four persons after E" places D at position 5 (4 steps after position 1 for E), which also satisfies "D attends before A" (A is at position 6).

• Placing the remaining person F at position 2 gives the order: $\text{E},\text{F},\text{B},\text{C},\text{D},\text{A},\text{G}$.

• Checking the final clue: "Three persons attend between A (pos 6) and F (pos 2)", which holds true (B, C, D are between them).

2. Compare the actual order with the alphabetical order:

• Actual Event Sequence: E, F, B, C, D, A, G

• Alphabetical Sequence: A, B, C, D, E, F, G

Comparing position by position:

Position 1: E ≠ A

Position 2: F ≠ B

Position 3: B ≠ C

Position 4: C ≠ D

Position 5: D ≠ E

Position 6: A ≠ F

Position 7: G = G (Unchanged)

Only one person (G) remains at the exact same position.