noun clause or adverb clause

Question

I read on Google books and exactly on this book: Applications of Grammar: Analysis of Effective Communication, Book 3 By Garry J. Moes, Ed Shewan

The following

Adverb clauses page 141

It is clear [that you do not know the facts]. (clause modifies the adjective "clear"
So, as a clause or any item grammar can qualify ( adjective ) = that item ( modifier ) no doubt = adverb

Others would say the clause ( that you do not know the facts) = noun clause appositive of the impersonal pronoun ( it )

( that you do not know the facts ) Is it noun clause or adverb clause ?

Answer 1

It is clear [that you do not know the facts].

The subordinate clause "that you do not know the facts" is neither a modifier not an appositive, but a declarative content clause.

The sentence is an extraposition construction with the dummy pronoun "it" as subject and the subordinate (that) clause as extraposed subject. The predicative complement of "be" is just "clear", just as it is in the non-extraposed "That you do not know the facts is clear".

Incidentally, I would suggest that you avoid the terms 'noun clause' and 'adverb clause'. Noun and adjective are parts of speech, not clause types.