De or het vallende?

The correct Dutch article is:

de vallende

How to use vallende

the vallendede vallende
this vallendedeze vallende
that vallendedie vallende
our vallendeonze vallende
your vallendejouw vallende
every vallendeelke vallende
which vallende?welke vallende?
a big vallende / the big vallendeeen grote vallende, de grote vallende

Dutch words ending in vallende

tegenvallende

In compound words, the last part decides the article. See the rule