Seven men, A, B, C, D, E, F and G are standing in a queue in that order. Each one is wearing a cap of a different colour like violet, indigo, blue, green, yellow, orange and red. D is able to see in front of him green and blue but not violet. E can see violet and yellow, but not red. G can see caps of all colours other than orange. If E is wearing an indigo-coloured cap, then the colour of the cap worn by F is

To solve this, we must understand that the men are in a queue from A at the front to G at the back. A person in a queue can see the caps of everyone standing in front of them, but not their own cap or the caps of those behind them.

G is at the very back in the seventh position. Since G can see all colors except orange, it means the orange cap must be worn by G himself because he cannot see his own cap.

D is in the fourth position and can see the caps of A, B, and C. D sees green and blue but not violet. This means violet must be worn by someone behind D, which would be E, F, or G. We already know G is wearing orange.

E is in the fifth position and can see the caps of A, B, C, and D. E sees violet and yellow, but not red. Since E can see violet but D could not, D must be the one wearing the violet cap.

E cannot see red, and since red is not among the colors seen by G, red must be worn by someone E cannot see. The only people E cannot see are himself and those behind him. E is wearing indigo as stated in the question. This leaves F and G. We already established G is wearing orange.

Therefore, the only person left who can be wearing the red cap is F. This is consistent with E not being able to see red, as F is standing behind E.

The correct answer is C.