Fill in the blank with the most appropriate preposition. The sentence is: The President will finally have a national memorial _____ his honour.

Introduction / Context:
This question tests the correct use of prepositions in a common English expression. The sentence talks about a national memorial created as a tribute to the President. In such contexts, English often uses fixed phrases, also called collocations, where only one specific preposition sounds natural and correct. Selecting the right option requires familiarity with the phrase in somebody's honour, which appears frequently in formal writing, speeches, and descriptions of commemorations or dedications.

Given Data / Assumptions:

• Sentence: The President will finally have a national memorial _____ his honour.
• Options: at, upon, in, on.
• We assume that the sentence refers to building or dedicating a memorial as a mark of respect to the President.
• The task is to choose the preposition that completes the standard expression correctly.

Concept / Approach:
The core concept is recognition of the fixed phrase in someone's honour, which means as a tribute to that person or to show respect for them. Prepositions in English are often not chosen by pure logic but by established usage. While at, upon, and on are valid prepositions in other contexts, the natural and idiomatic collocation with honour in this tribute sense is in his honour. The approach is to recall the phrase from reading and listening experience or to eliminate options that do not form a familiar or grammatically sound combination with honour in this context.

Step-by-Step Solution:
Step 1: Read the full sentence with each option to see which sounds natural. Step 2: Try at: a national memorial at his honour sounds incorrect and does not express tribute. Step 3: Try upon: a national memorial upon his honour is also unnatural and not used idiomatically. Step 4: Try in: a national memorial in his honour is a familiar and standard phrase indicating a memorial created as a mark of respect. Step 5: Try on: a national memorial on his honour also sounds wrong and is not a recognised expression. Step 6: Conclude that in is the only option that forms the correct phrase in his honour.

Verification / Alternative check:
To verify, consider other sentences that describe events or objects dedicated to people. For example, they organised a concert in her honour, a scholarship was created in his honour, and the dinner was held in their honour. In each case, the preposition in is used before honour to show that the event or object is meant as a tribute. By comparing these standard expressions with the sentence in the question, we confirm that in his honour is the correct and natural choice. No other preposition from the options matches established usage in this context.

Why Other Options Are Wrong:
at: This preposition is often used for locations or points in time, such as at the station or at five o clock, and does not fit the phrase with honour here.
upon: This is a more formal version of on used in certain structures, but the expression upon his honour is not used to describe a memorial dedicated as a tribute.
on: This might be used in other collocations like based on or depend on, but on his honour in this context does not express the intended meaning of tribute.

Common Pitfalls:
A common mistake is trying to apply direct translation from a mother tongue, where a different preposition may be used with a similar noun. Another pitfall is relying purely on what sounds formal without checking whether the combination is actually used in standard English. Prepositions in fixed phrases must often be memorised as whole units, such as in honour of, in memory of, or in recognition of. Regular reading and listening to formal English helps learners internalise these collocations and avoid incorrect combinations.

Final Answer:
The correct preposition is in, so the sentence should read: The President will finally have a national memorial in his honour.