Bill Reynolds wrote:

I have a small patch (3"x3" ) of a black mould on a piece of drywall.

What is a good way to kill it?

TIA
Normal household cleaner with a little bleach, risne, dry. Where is it
and why? Just a damp area with poor air circulation? Roof leak? If
roof leak, take care of cause. A badly aimed AC vent can cause
condensation on a wall and just requires it be redirected.

Mold spores are everywhere, and just need some moisture and nutrients to
grow. Don't panic.