Explanation:
The correct answer is option 'B', False. Oxygen and nitrogen do not make up 78% of air. Let's break down the components of air and their percentages:

1. Nitrogen:
Nitrogen is the most abundant gas in the Earth's atmosphere, accounting for approximately 78% of the air. It is an essential element for living organisms and plays a crucial role in various biological and chemical processes.

2. Oxygen:
Oxygen is the second most abundant gas in the atmosphere, making up approximately 21% of the air. It is vital for the survival of most organisms, as it is involved in the process of respiration, where energy is released from food.

3. Other Gases:
While nitrogen and oxygen are the two main components of air, there are also other gases present in smaller amounts:

- Carbon Dioxide (CO2): It constitutes about 0.04% of the air and is essential for photosynthesis in plants.
- Argon (Ar): Argon makes up about 0.93% of the air and is an inert gas, meaning it does not readily react with other substances.
- Trace Gases: There are also trace amounts of other gases like neon, helium, methane, ozone, and water vapor present in the atmosphere. These gases collectively contribute to less than 0.1% of the air.

Conclusion:
To summarize, while nitrogen and oxygen are the two main components of air, nitrogen accounts for approximately 78% of the air, and oxygen makes up about 21%. The remaining percentage is occupied by other gases, including carbon dioxide, argon, and trace gases. Therefore, the statement that oxygen and nitrogen make up 78% of air is false.