Arrange the following words in proper dictionary order and choose the option that shows the correct sequence: 1. SINISTER 2. SINUOUS 3. SINHALESE 4. SINUSITIS 5. SINECURE.

Introduction / Context:
This question requires you to arrange five words that all start with the letters SIN in dictionary order. Such problems test attention to detail when dealing with very similar looking words. You must compare the letters of SINECURE, SINISTER, SINHALESE, SINUOUS, and SINUSITIS step by step and then select the option that represents the correct sequence of their indices.

Given Data / Assumptions:

• Indexed words: 1. SINISTER, 2. SINUOUS, 3. SINHALESE, 4. SINUSITIS, 5. SINECURE.
• All words start with S I N, so the ordering depends on letters from the fourth position onward.
• Standard dictionary or alphabetical ordering applies.
• Options contain only sequences of indices, not the words themselves.

Concept / Approach:
To determine dictionary order, compare words letter by letter from left to right. When the first three letters are identical, as is the case here, you focus on the fourth letter, then the fifth, and so on until you find a difference. The word whose differing letter comes earlier in the alphabet will appear earlier in the dictionary. By repeating this process for all five words, you can derive their correct order.

Step-by-Step Solution:
Step 1: Write all five words: SINECURE, SINISTER, SINHALESE, SINUOUS, SINUSITIS.Step 2: After the common prefix SIN, the fourth letters are: E in SINECURE, I in SINISTER, H in SINHALESE, U in SINUOUS, and U in SINUSITIS.Step 3: Alphabetically, E comes first, followed by H, then I, and finally U. So SINECURE (5) must come first.Step 4: Next compare SINHALESE and SINISTER because their fourth letters H and I come after E but before U. Since H comes before I, SINHALESE (3) comes before SINISTER (1).Step 5: Now consider SINUOUS and SINUSITIS. Both share the prefix SINU. After that, SINUOUS contains O and SINUSITIS contains S. Because O comes before S, SINUOUS (2) comes before SINUSITIS (4).Step 6: Combining these findings, the full dictionary order is SINECURE (5), SINHALESE (3), SINISTER (1), SINUOUS (2), SINUSITIS (4), which corresponds to the index sequence 5, 3, 1, 2, 4.

Verification / Alternative check:
You can quickly verify by grouping words by their fourth letter: those with E, H, I, and U. The U group contains SINUOUS and SINUSITIS and must come last within the overall list. Next, checking the fifth letters inside the U group confirms that SINUOUS comes before SINUSITIS. Checking the relative order of SINECURE, SINHALESE, and SINISTER using the fourth letters E, H, and I confirms their placement as first, second, and third. A final comparison against the answer choices shows that only option 5, 3, 1, 2, 4 matches this ordering.

Why Other Options Are Wrong:
Option 5, 3, 2, 4, 1 is incorrect because it places SINUOUS and SINUSITIS before SINISTER, ignoring the fact that I comes before U.Option 5, 2, 4, 3, 1 and option 5, 2, 1, 3, 4 are wrong because they misorder SINHALESE and SINISTER, and also misplace SINUOUS relative to SINUSITIS.

Common Pitfalls:
The main difficulty in such questions lies in the similarity of the initial letters. Students may stop comparing too early or rely on intuition rather than a full letter by letter comparison. Another common error is failing to treat U group words separately and not checking their letters beyond the shared prefix. Writing down each word and underlining the first differing letter is a practical technique to avoid confusion and ensure the correct sequence.

Final Answer:
The correct dictionary order corresponds to the index sequence 5, 3, 1, 2, 4.