The grammatical nature of "mondai naku"


In the sentence:

> でも今は問題なく食べることができます  
>  Demo ima wa mondai naku taberu koto ga dekimasu"

what is the grammatical nature of "mondai naku"? Is it a noun, an adjective or
an adverb?




It's _adverbial_ , i.e., it modifies a verb. In general, the ku-form of an
adjective is also known as the adverbial form.

  * この車は速 **く** 走る。(adverbial)  
This car runs _fast_.

  * 速 **い** 電車 (adjectival)  
a _fast_ car

ない is a bit special in that it can take certain nouns and work like a suffix
meaning "-less(ly)", but the resulting phrase is still grammatically an
adjective, so its ku-form is adverbial. You can think 問題ない is a [distinct
adjective](https://jisho.org/word/%E5%95%8F%E9%A1%8C%E3%81%AA%E3%81%84).

Similar example:

  * 変わりない日々  
uneventful days

  * 変わりなく日々を過ごしています。  
I spend days uneventfully.

