The average atmospheric pressure at sea level is 760 mmHg. This is commonly referred to as 1 atmosphere (atm) of pressure. Atmospheric pressure is the force per unit area exerted on a surface by the weight of the air above it. It is affected by various factors such as altitude, temperature, and weather conditions.

Factors Affecting Atmospheric Pressure:

1. Altitude: Atmospheric pressure decreases with increasing altitude. This is because there is less air above a given point at higher altitudes, resulting in lower atmospheric pressure. At sea level, where the majority of the Earth's surface is located, the weight of the air column above is greatest, leading to higher atmospheric pressure.

2. Temperature: Temperature also affects atmospheric pressure. As temperature increases, the air molecules gain more energy and move faster, resulting in increased pressure. Conversely, as temperature decreases, the air molecules slow down and the pressure decreases. However, the impact of temperature on atmospheric pressure is less significant compared to altitude.

3. Weather Conditions: Weather conditions such as high and low-pressure systems can also affect atmospheric pressure. High-pressure systems, also known as anticyclones, are associated with clear skies and fair weather. They occur when the air is sinking, leading to increased atmospheric pressure. Low-pressure systems, or cyclones, are associated with cloudy and stormy weather. They occur when the air is rising and result in lower atmospheric pressure.

Explanation of the Correct Answer:

The correct answer to this question is option 'C' which states that the average atmospheric pressure at sea level is 760 mmHg. This value represents the normal atmospheric pressure at sea level under standard conditions. It is equivalent to 1 atm or 101.3 kilopascals (kPa). This value is widely accepted and used as a reference for atmospheric pressure calculations and measurements.

Conclusion:

Understanding the average atmospheric pressure at sea level is important in various fields such as meteorology, aviation, and scuba diving. It provides a baseline for comparing and interpreting pressure measurements at different locations and altitudes. The average atmospheric pressure of 760 mmHg at sea level is a result of the weight of the air column above and is influenced by altitude, temperature, and weather conditions.