The correct option is C Selection of 6 officers out of 13 officers for post of major general of army.
Combination involves selection of "n" different things out of m different things.
Arrangements of things are not done.
Also, order of selection does not matter.
Option1–––––––––:Arrangement of 5 chocolates taken 3 at a time.
This is a case of arrangements, which is not allowed in combination.
Option2–––––––––: Permutation of 11 different things without repetition.
Permutations itself means arrangements of things.
So, this is also not example of combination.
Option3–––––––––: Selection of 6 officers out of 13 officers for post of major general of army.
This is a selection process which is also known as combination.
So, this is example of combination.