Read each sentence to find out whether there is any grammatical or idiomatic error in it. The error, if any, will be in one part of the sentence. The corresponding letter of that part is the answer. If the given sentence is grammatically and contextually correct, then choose “No error” as the correct answer. (Ignore errors of punctuation, if any.)

Both Ravi as well as (A) / his brother are going (B) / to attend the (C) / wedding of their cousin. (D)

Correct option is C

The sentence has a grammatical error in part (A).
The sentence is discussing the attendance of both Ravi and his brother at a wedding. The conjunction "and" is used to connect the two subjects "Ravi" and "his brother" in a parallel structure, indicating that both of them are going to attend the wedding.
Therefore, the correct form should be "Ravi and his brother" without the use of parentheses.
Hence, the correct sentence formed will be "Both Ravi and his brother are going to attend the wedding of their cousin."