Which of the following sentences is punctuated correctly when using the linking word "however" between two independent clauses?

Introduction / Context:
This question tests your knowledge of punctuation when connecting two independent clauses with the adverb however. In formal writing, however used in this way is often placed after a semicolon and followed by a comma. Choosing the correctly punctuated sentence helps demonstrate understanding of both clause structure and the role of conjunctive adverbs.

Given Data / Assumptions:
- All options contain two ideas: the planned length of the conference and the actual length. - The word however shows contrast between the expectation and the reality. - Both parts are independent clauses that could stand alone as sentences. - We are looking for the standard punctuation pattern in this context.

Concept / Approach:
When a conjunctive adverb such as however, therefore, or moreover connects two independent clauses in a single sentence, the usual pattern in formal English is clause one, a semicolon, the adverb, a comma, then clause two. This structure both separates the clauses correctly and signals the contrast or relationship. A comma before however alone creates a comma splice, and missing the comma after however makes the sentence harder to read.

Step-by-Step Solution:
Step 1: Recognise that "The conference was only supposed to be an hour" and "it ran for nearly two and half hours" are both complete clauses. Step 2: Look at option a: "The conference was only supposed to be an hour; however, it ran for nearly two and half hours." Here, a semicolon precedes however and a comma follows it. This matches the standard pattern. Step 3: Option b uses a comma before however and a semicolon after it: "The conference was only supposed to be an hour, however; it ran..." This creates a comma splice error before however and misuses punctuation after it. Step 4: Option c splits the clauses with a full stop but then starts however with a lowercase letter: "The conference was only supposed to be an hour. however, it ran..." This is incorrect because a new sentence must begin with a capital letter. Step 5: Option d uses a semicolon before however but omits the comma after it: "The conference was only supposed to be an hour; however it ran..." This is not the usual recommended form and may cause a slight pause problem for the reader. Step 6: Therefore, option a is the only sentence that follows the widely accepted rule for punctuating however between two independent clauses.

Verification / Alternative check:
You can check grammar references or recall similar constructions you have seen in textbooks: "He wanted to join us; however, he was busy." Notice the pattern of semicolon and comma. If you replace however with and or but, you would use just a comma and a coordinating conjunction, not a semicolon. This confirms that the special punctuation with however is semicolon before and comma after in a single combined sentence, exactly as in option a.

Why Other Options Are Wrong:
Option b: The comma before however creates a run on sentence, and placing a semicolon after however is not standard. Option c: Starts a new sentence after the full stop but incorrectly leaves however in lowercase. Option d: Omits the comma after however, which is recommended to show a clear pause and separate the adverb from the second clause.

Common Pitfalls:
Many learners treat however like a simple conjunction such as but and use only a comma before it. This often leads to comma splices. Others are unsure whether to start a new sentence or use a semicolon. A good rule is to remember that however is a conjunctive adverb, not a conjunction, so it needs stronger punctuation to join independent clauses. Practising a few model sentences with however will make the correct pattern more familiar.

Final Answer:
The correctly punctuated sentence is "The conference was only supposed to be an hour; however, it ran for nearly two and half hours."