He begged "that his life might be spared" The part of the sentence is a

A Adverb Clause

B Noun Clause

C. Adjective Phrase

D. Noun Phrase

B Noun Clause

Explanation:

A noun clause is a dependent clause that acts as a noun.

"that his life might be spared" acts as a noun.

We may say:

"He begged something"; for example, "he begged their forgiveness."

So we use a noun with the verb begged. Therefore, this part of the sentence (that his life might be spared) is a noun clause.