De or het volumedaling?

The correct Dutch article is:

de volumedaling

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

How to use volumedaling

the volumedalingde volumedaling
this volumedalingdeze volumedaling
that volumedalingdie volumedaling
our volumedalingonze volumedaling
your volumedalingjouw volumedaling
every volumedalingelke volumedaling
which volumedaling?welke volumedaling?
a big volumedaling / the big volumedalingeen grote volumedaling, de grote volumedaling