Explanation:

Correct answer is (a). In the given sentence, the part given in bold has error in it. Usage of 'a' before 'right' is erroneous as 'right' is an adjective and not a noun.  The correct sentence would be: He is quite right in his approach towards solving this issue but the higher management disagrees with him. Quiet right in option C is incorrect since quiet means calm and composed and it is completely out of context in the given statement. It makes option A the correct choice among the given options.