Answer:

Introduction:
When storing a fresh sample of oil for a long time, it is important to prevent its degradation or oxidation. This can be achieved by using an appropriate gas to create an inert atmosphere that minimizes contact with oxygen, moisture, and other reactive substances. Among the options given, nitrogen or helium are the most suitable gases for this purpose.

Explanation:
Nitrogen:
- Nitrogen is an inert gas, meaning it is chemically unreactive and does not readily react with other substances.
- It is abundantly available in the atmosphere and is commonly used for various industrial and laboratory applications.
- When used for storing oil samples, nitrogen replaces the oxygen in the storage container, thus creating an oxygen-free environment.
- This prevents oxidation and slows down the degradation of the oil, helping to maintain its freshness and quality over a long period of time.

Helium:
- Helium is another inert gas that is chemically stable and does not react with other substances.
- It is lighter than air and has low solubility in most liquids, including oil.
- When used as a storage gas, helium creates a protective blanket over the oil sample, preventing oxygen and moisture from coming into contact with the oil.
- This helps to maintain the oil's freshness and prevents degradation or oxidation.

Comparison:
Both nitrogen and helium are suitable for storing oil samples for a long time. However, there are a few key differences between the two gases:

- Availability: Nitrogen is more readily available and less expensive compared to helium, which is relatively rare and more expensive.

- Density: Helium is lighter than air and has low solubility in oil, making it more effective in creating a protective blanket over the oil sample.

- Cost: Nitrogen is generally more cost-effective and practical for most applications. Helium is typically reserved for specialized or high-value samples due to its higher cost.

Conclusion:
In conclusion, nitrogen or helium can be used for the storage of fresh samples of oil for a long time. Both gases create an inert atmosphere that prevents oxidation and degradation of the oil. Nitrogen is more commonly used due to its availability and cost-effectiveness, while helium is preferred for specialized or high-value samples.