De or het gasuitwisseling?

The correct Dutch article is:

de gasuitwisseling

Rule Words ending in -ing: almost always de. See the rule

How to use gasuitwisseling

the gasuitwisselingde gasuitwisseling
this gasuitwisselingdeze gasuitwisseling
that gasuitwisselingdie gasuitwisseling
our gasuitwisselingonze gasuitwisseling
your gasuitwisselingjouw gasuitwisseling
every gasuitwisselingelke gasuitwisseling
which gasuitwisseling?welke gasuitwisseling?
a big gasuitwisseling / the big gasuitwisselingeen grote gasuitwisseling, de grote gasuitwisseling