The Chairman of a big company visits one department on Monday of every week except for the Monday of third week of every month. When did he visit the Purchase department ? I. He visited Accounts department in the second week of September after having visited Purchase department on the earlier occasion. II. He had visited Purchase department immediately after visiting Stores department but before visiting Accounts department.

From statement I. we can conclude that the Chairman visited Purchase department on Monday of the first week of September. So, I alone is sufficient, The time of visit of no department is mentioned in II. which is, therefore, insufficient