De or het manteling?

The correct Dutch article is:

de manteling

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

How to use manteling

the mantelingde manteling
this mantelingdeze manteling
that mantelingdie manteling
our mantelingonze manteling
your mantelingjouw manteling
every mantelingelke manteling
which manteling?welke manteling?
a big manteling / the big mantelingeen grote manteling, de grote manteling

Dutch words ending in manteling

ontmanteling

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