The following sentence has been split into four segments. Identify the segment that contains a grammatical error.
When Serena / will arrive, / she will / call you.

Correct option is A

Explanation:
In time clauses (using when, after, before, etc.), we do not use future tense, even if referring to future time.
Correct Sentence:
When Serena arrives, she will call you.
Grammar Rule:
After conjunctions like when, before, after, until, use simple present, not future, even for future actions.
When he comes, we will leave.