Final answer:
The phrase 'troubles in his exam' is a phrase, as it does not contain a subject and a verb to form a complete clause.
Step-by-step explanation:
In the sentence 'He faced a lot of troubles in his exam', the phrase 'troubles in his exam' is a phrase.
A phrase is defined as any group of words that functions as a unit within a sentence. It can be missing either a subject or a verb. In this case, 'troubles in his exam' is a group of words that functions together, but it does not contain a subject and a verb to form a complete clause.
Therefore, the correct answer is phrase (b).