Answer:
is this English i read this before?/
Explanation:
The italicized word (magnitude) in the sentence can best be matched by the word: size. This is referring to the size of the disaster, that it is hard to imagine something happening on that size scale.
Nonrestrictive because the sentence you "My brother who lives in Hawaii is a surfer" is not restrictive but the answer to your question is = Nonrestrictive.
“About Mars” is the Adjective Phrase.
Adjective phrase describes “what kind of which ones”
So for example here
“After school, I looked for books about Mars.”
“About Mars” describes the kind of books so that makes it an Adjective phrase.
I hope this helps.