Data Sufficiency — Weekly Monday visits (third Monday skipped): When did the Chairman visit the Purchase department? Statements: I. He visited the Accounts department in the second week of September, after having visited the Purchase department on the earlier occasion. II. He visited the Purchase department immediately after visiting Stores, but before visiting Accounts.

Introduction / Context:
The Chairman visits exactly one department every Monday, but skips the Monday of the third week of each month. We must identify when he visited the Purchase department, given partial sequencing information. In data sufficiency, we only need to know whether a unique timing can be deduced, not necessarily the full calendar date.

Given Data / Assumptions:

• Visit rule: every Monday except the third Monday of the month (no visit that week).
• I: Accounts was visited in the 2nd week of September, and Purchase was visited on the earlier occasion.
• II: Purchase occurred immediately after Stores and before Accounts (ordering constraint only).

Concept / Approach:
Translate the “earlier occasion” in Statement I using the weekly pattern. Mondays progress week by week with a regular cadence; between the 1st and 2nd Monday there is no skipped Monday. Hence the “earlier occasion” before the 2nd-week Monday is the 1st-week Monday of September.

Step-by-Step Solution:
From I: If Accounts is in Week-2 Monday of September, the immediately previous visit is Week-1 Monday of September (no skip occurs between week 1 and week 2). That earlier visit is stated to be Purchase.Therefore, Purchase was visited on the first Monday of September.Statement II adds an ordering Stores → Purchase → Accounts, but without any calendar anchor, II alone cannot place Purchase in a specific week.

Verification / Alternative check:
The “skip third Monday” rule does not affect positioning between week 1 and week 2. Thus, the conclusion from I is robust and unique.

Why Other Options Are Wrong:

• II alone: Pure ordering—no week/date can be fixed.
• Either / Both: I alone suffices; adding II is unnecessary.
• Neither: Incorrect because I alone works.

Common Pitfalls:

• Misreading “earlier occasion” as an arbitrary earlier month rather than the immediately previous Monday visit.
• Letting the “third-Monday skip” confuse the straightforward week-1 to week-2 progression.

Final Answer:
I alone is sufficient while II alone is not sufficient