From the following statements on air pressure, choose which is the correct one:

Air pressure is the weight of air molecules pressing down on the Earth.

• The pressure of the air molecules changes as you move upward from sea level into the atmosphere.
• The highest pressure is at sea level where the density of the air molecules is the greatest.

Important Points 

1. The Air pressure decreases with height. Air pressure is higher at lower altitudes. Air density is higher at lower altitudes.
2. There is more space between air molecules at higher altitudes. There is less oxygen to breathe at the top of a high mountain than there is at sea level.

Additional Information 

1. As air rises, the pressure decreases. It is this lower pressure at higher altitudes that causes the temperature to be colder on top of a mountain than at sea level.
2. Air pressure is the highest at sea level.

Hence, Air pressure decreases when you go upward or mountains.