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

Let's break down the clues step-by-step:

1. Men are A, B, C, D, E, F, G in a queue (from front to back). A person can see caps of those in front of them.
2. Colours: Violet (V), Indigo (I), Blue (B), Green (G), Yellow (Y), Orange (O), Red (R).

Given: E is wearing an Indigo (I) coloured cap. So, E = I.

Clue 1: D is able to see in front of him Green and Blue, but not Violet.

• D sees A, B, C. So, Green and Blue are among A, B, C.
• D does not see Violet. This means Violet is either D's own cap, or the cap of someone behind D (E, F, G).

Clue 2: E can see Violet and Yellow, but not Red.

• E sees A, B, C, D. So, Violet and Yellow are among A, B, C, D.
• E does not see Red. This means Red is either E's own cap, or the cap of someone behind E (F, G).
• Since E is wearing Indigo, Red cannot be E. So Red is F or G.

Combining Clue 1 and Clue 2 for Violet:

• From Clue 1: Violet is D, E, F, or G.
• From Clue 2: Violet is A, B, C, or D.
• The only position common to both is D. Therefore, D must be wearing the Violet cap. So, D = V.

Now we have: D = V and E = I.

Let's re-evaluate with D=V and E=I:

• Clue 1 (D sees Green and Blue, but not Violet): D (Violet) cannot see his own cap, which is consistent. A, B, C wear Green and Blue (and one other colour).
• Clue 2 (E sees Violet and Yellow, but not Red): E (Indigo) sees D (Violet), which is consistent. E also sees Yellow, so Yellow is among A, B, C. E does not see Red, so Red is F or G.

From the above, we know:

• A, B, C wear Green, Blue, Yellow (these are 3 distinct colours for 3 people).
• D wears Violet.
• E wears Indigo.
• F and G wear the remaining two colours, which are Orange and Red.

Clue 3: G can see caps of all colours other than Orange.

• G is at the very end of the queue. G sees A, B, C, D, E, F.
• If G sees all colours except Orange, it means Orange must be G's own cap. So, G = O.

Now we have:

• D = Violet
• E = Indigo
• G = Orange

The colours used are Violet, Indigo, Orange. The remaining colours are Blue, Green, Yellow, Red. The remaining people are A, B, C, F.

We established that A, B, C wear Green, Blue, Yellow. This leaves Red as the only remaining colour for F.

Therefore, F wears Red.

The final answer is C) Red.