In English vocabulary, choose the correct one word substitute for "a man who collects old and new coins".

Introduction / Context:
One word substitution questions often focus on hobbies, professions, and areas of study. The phrase here, a man who collects old and new coins, points to a very specific hobby and field of study related to currency. In English, there is a technical term for people who study or collect coins, medals, and related objects, and this term is widely used in exam questions and general knowledge discussions.

Given Data / Assumptions:

• The person collects both old and new coins as a hobby or serious interest.
• The options are names of people linked with different subjects.
• We need the precise term from English vocabulary.
• The question targets knowledge of specialist hobby names.

Concept / Approach:
The correct term for a person who studies or collects coins is numismatist. Numismatics is the study of coins, paper money, and medals. A geologist studies rocks and the Earth's structure, an archaeologist studies human history through excavated sites and artefacts, and a zoologist studies animals. Although old coins sometimes appear in archaeological digs, the collector of coins as such is called a numismatist, which directly matches the phrase given.

Step-by-Step Solution:
Step 1: Identify the core activity in the phrase, namely collecting coins. Step 2: Recall the term numismatics, which is the study of coins and currency. Step 3: Link numismatics with numismatist, the person who pursues this activity. Step 4: Compare with other options and see that they refer to different academic fields. Step 5: Choose numismatist as the only accurate one word substitute.

Verification / Alternative check:
Think of typical sentences like He is a numismatist who has a rare collection of ancient coins. This sentence clearly and naturally describes someone who collects coins. If you try to use geologist or zoologist in the same sentence, the meaning becomes absurd. Archaeologist is closer because archaeologists sometimes find coins, but their main job is to study past human cultures, not coins alone. This comparison confirms that numismatist is the precise word you need in this question.

Why Other Options Are Wrong:
Geologist studies rocks, minerals, and the Earth's physical structure, not collections of coins.

Archaeologist investigates human history and prehistory through excavation and analysis of artefacts and remains, only occasionally dealing with coins.

Zoologist is concerned with the scientific study of animals, their behaviour, and their classification, which is unrelated to coins.

Common Pitfalls:
Sometimes learners confuse numismatist with philatelist, the latter being the word for someone who collects stamps. Both hobbies involve small collectible items, so the terms can be mixed up. Remember that numismatics starts with n like notes and coins, while philately relates to postage and stamps. This simple association can help you quickly pick the correct option in exam conditions.

Final Answer:
The correct one word substitute is Numismatist.