It's a colony of ants or a nest of ants. If we say an ants' colony, or ants' nest, it's the place where they live.
There is no standard collective noun for a group of reflections.
The noun 'reflection' is not a standard collective noun.
The noun 'choir' is a collective noun for: a choir of singers.
The noun 'crowd' is a standard collective noun for a crowd of people, a crowd of onlookers.
I believe that word is 'litter'.
No. A battalion is a collection of soldiers, or the physical sum of the soldiers and their equipment.
All we know is that he was a Greek man of great strength.
The noun casserole is a countable noun. Example:
We have two casseroles, one tuna casserole and one chicken casserole.
The noun sheet is a countable noun. The plural form is sheets.
Transport is both countable and uncountable as a noun.
The standard collective noun is: an audience of listeners