Using Bayesian probability theorem,
probability that a chip is shipped by company X = 5/9
probability that a chip is shipped by company Y = 4/9
probability of getting defective piece from company X = 1/5
probability of getting defective piece from company Y = 2/4
Hence, probability that if the chosen chip is found to be defective, then chip came from the company Y is
===> (4/9 * 2/4) / ((4/9 * 2/4) + (5/9 * 1/5))
===> 2/3
Answer is C