Fill in the blank with the most appropriate noun: "Arun's financial ______________ has helped him earn a fortune on the stock market."

Introduction / Context:
This sentence completion question focuses on vocabulary and collocation. It describes Arun, who has earned a fortune on the stock market, and attributes his success to a particular quality related to finance. The blank must be filled with a noun that accurately and naturally combines with financial to describe specialised knowledge and skill.

Given Data / Assumptions:

- Sentence: Arun's financial ______________ has helped him earn a fortune on the stock market. - Options: dexterity, readiness, expertise, knack. - The context is about success in investing, which normally depends on knowledge, analysis, and informed decisions. - The noun must form a common and natural phrase with financial.

Concept / Approach:
The phrase financial expertise is widely used to describe deep knowledge and professional skill in financial matters, such as investment, risk management, and analysis. Expertise itself means expert skill or knowledge in a particular field. While dexterity, readiness, and knack can refer to abilities, they do not collocate as strongly with financial in standard English. Therefore, expertise best fits both the meaning and the typical usage pattern.

Step-by-Step Solution:
Step 1: Interpret the sentence logically. Earning a fortune on the stock market usually requires specialised knowledge and experience, not just quick reactions. Step 2: Look at expertise, which directly means expert skill or knowledge in a specific area, and see how well financial expertise fits the context. Step 3: Consider dexterity, which more often refers to physical skill or quickness with the hands, though it can sometimes be used figuratively. Step 4: Examine readiness, which suggests being prepared or willing, but does not by itself convey the idea of high level knowledge. Step 5: Check knack, which means a natural talent or ability, but financial knack is not a strongly established collocation and sounds informal. Step 6: Conclude that expertise is both semantically accurate and idiomatically natural here.

Verification / Alternative check:
Substitute each option into the sentence. Arun's financial expertise has helped him earn a fortune on the stock market sounds very natural and could easily appear in a news article or financial profile. Arun's financial dexterity is possible but less common and may suggest quick handling of transactions rather than deep understanding. Arun's financial readiness sounds odd, as readiness is not normally used with financial in this way. Arun's financial knack is informal and unusual. This comparison confirms that expertise is the best choice.

Why Other Options Are Wrong:
Dexterity focuses on physical skill or sometimes on nimbleness of mind, but the standard phrase is manual dexterity or mental dexterity, not financial dexterity. Readiness describes a state of being prepared but does not inherently indicate knowledge or skill, and the phrase financial readiness is generally used for availability of funds, not for individual ability. Knack suggests a natural talent but is less formal and does not combine strongly with financial in conventional usage.

Common Pitfalls:
Some learners rely mainly on the idea of ability and may select knack without considering how often it appears in collocation with financial. Others may be attracted to dexterity because it sounds sophisticated. A better approach is to consider both meaning and common phrase patterns that you have seen in reliable reading materials. Financial expertise is a widely used expression in business and finance reporting and therefore is the safest and most accurate choice.

Final Answer:
expertise correctly completes the sentence: Arun's financial expertise has helped him earn a fortune on the stock market.