De or het fenoloplossing?

The correct Dutch article is:

de fenoloplossing

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

How to use fenoloplossing

the fenoloplossingde fenoloplossing
this fenoloplossingdeze fenoloplossing
that fenoloplossingdie fenoloplossing
our fenoloplossingonze fenoloplossing
your fenoloplossingjouw fenoloplossing
every fenoloplossingelke fenoloplossing
which fenoloplossing?welke fenoloplossing?
a big fenoloplossing / the big fenoloplossingeen grote fenoloplossing, de grote fenoloplossing