The correct answer is option 4: "Temperature decreases with height in the troposphere at an average rate of 6.4 C per kilometer."

Option 1 states that temperature decreases with height in the stratosphere. However, this is not accurate as the temperature in the stratosphere actually increases with height.

Option 2 claims that the temperature is constant at different heights in the stratosphere. This statement is also incorrect as the temperature in the stratosphere does not remain constant with height.

Option 3 suggests that the temperature increases with height in the troposphere at an average rate of 6.5 C per kilometer. This statement is similar to the actual fact, but the average rate of temperature increase in the troposphere is 6.4 C per kilometer, not 6.5 C.

Therefore, the correct statement is that temperature decreases with height in the troposphere at an average rate of 6.4 C per kilometer.