The question asks us about the environmental temperature lapse rate per 1000 m of ascent. This refers to how much the temperature decreases as we ascend in altitude by 1000 m.

Option 1 states that the temperature lapse rate per 1000 m of ascent is 4.6°C. Option 2 states it is 5.8°C. Option 3 states it is 6.4°C. Option 4 states it is 6.8°C.

The correct answer is option 3, which states that the temperature lapse rate per 1000 m of ascent is 6.4°C. This means that for every 1000 m of ascent in altitude, the temperature decreases by 6.4°C.

It is important to note that the lapse rate can vary depending on various factors such as geographical location and weather conditions. However, based on the information provided in the question, option 3 is the correct answer.