Arrange the following words in the sequence in which they occur in a standard English dictionary and then select the correct numeric code: 1. Opaque 2. Omission 3. Only 4. Onset 5. Omit.

Introduction / Context:
This dictionary order question uses five words beginning with the letter O. You must determine their correct dictionary sequence and then choose the numeric pattern corresponding to that order. This is a staple type of verbal reasoning problem that develops attention to spelling and alphabetical comparison beyond the first or second letters of each word.

Given Data / Assumptions:

• Words: 1. Opaque, 2. Omission, 3. Only, 4. Onset, 5. Omit.
• All words start with 'O', so we must compare letters from the second position onward.
• Standard English dictionary ordering is assumed.

Concept / Approach:
We compare words alphabetically, letter by letter. When words share the same first letters, we examine subsequent letters until a difference is found. If one word is an exact prefix of another, the shorter word comes first. Here, some words share the first two letters 'Om' or 'On', while Opaque begins with 'Op'. Grouping by the first two letters simplifies the reasoning and helps us avoid confusion.

Step-by-Step Solution:
Step 1: Write the words with their first two letters noted: Opaque (Op...), Omission (Om...), Omit (Om...), Only (Onl...), Onset (Ons...). Step 2: Compare second letters: a, m, m, n, n for each word respectively. Alphabetically, 'a' comes first, then 'm', then 'n'. So Opaque (1) with 'Op' actually has second letter 'p', but we are comparing correctly as: Opaque (Op), Omission (Om), Omit (Om), Only (On), Onset (On). Therefore, Om words come before On words, and both come before Op words because 'm' precedes 'n' and 'p'. Step 3: Among Omission (2) and Omit (5) which both start with 'Omi', we compare further letters. Omission continues with 'ssion' while Omit ends after 't'. After the shared prefix 'omi', the next letters are s and t. Since s comes before t, Omission (2) appears before Omit (5). Step 4: Next, compare Only (3) and Onset (4), both starting with 'On'. After 'on', Only has 'l' and Onset has 's'. Since l comes before s, Only (3) comes before Onset (4). Step 5: Finally, we place Opaque (1), which begins with 'Op'. Since 'p' comes after 'm' and 'n', Opaque must follow all Om and On words. Thus the full order is: Omission (2), Omit (5), Only (3), Onset (4), Opaque (1), giving code 25341.

Verification / Alternative check:
A simpler verification is to group words by their first two letters explicitly: Om (Omission, Omit), On (Only, Onset) and Op (Opaque). Arrange these groups alphabetically as Om, On, Op. Within Om, compare the next differing letter after 'omi' to get Omission then Omit. Within On, compare letters after 'on' to get Only then Onset. Append Op last. This regrouping leads directly to the same final sequence 2, 5, 3, 4, 1.

Why Other Options Are Wrong:
Option 51243 begins with Omit, which should follow Omission rather than precede it. Option 42513 and 21354 also place Opaque incorrectly or break the internal ordering within Om and On clusters. They do not respect the correct alphabetical relationships determined above. Only 25341 aligns perfectly with the dictionary ordering of the five words.

Common Pitfalls:
Candidates sometimes incorrectly assume that Op words come before Om or On because they appear earlier in the given list. Another frequent mistake is not checking carefully where Opaque belongs, due to confusion between the vowel sequence after O. To avoid such issues, always rely on strict alphabetical comparison and ignore the original listing order. Grouping by initial letter pairs is a very helpful strategy in similar questions.

Final Answer:
The correct dictionary sequence corresponds to the numeric code 25341, so that is the correct answer.