Identify the clause of the underlined part in the given sentence.

All that glitters is not gold.

Correct option is B

The underlined part “that glitters” is an Adjective Clause.

• A clause is a group of words that contains a subject and a verb.
• Adjective Clause:
  An adjective clause is a dependent (subordinate) clause that modifies a noun or pronoun, telling us which one or what kind.
• In the sentence, "that glitters" describes or modifies the noun "all" (referring to things), telling us which things are being talked about — those that glitter.
• It answers the question "Which all?" — those that glitter.

Thus, "that glitters" functions exactly like an adjective does, modifying a noun, and therefore, it is an Adjective Clause.