What is the collective noun of mop?

There isn't a widely accepted or commonly used collective noun for a group of mops.

You could use more descriptive phrases like:

* A set of mops

* A collection of mops

* A pile of mops

* A supply of mops

You could also get creative and use phrases like:

* A squadron of mops (for a group of mops working together)

* A flurry of mops (for a chaotic group of mops)

* A swish of mops (for a group of mops being used)

Ultimately, the best phrase to use depends on the context and the desired effect.