What is the approximate rate unsaturated air will cool when flowing upslope?

The correct choice is based on the standard environmental lapse rate, which describes how temperature typically decreases with altitude in the troposphere under normal atmospheric conditions. When unsaturated air rises, it cools at an approximate rate of 3 degrees Celsius for every 1,000 feet of ascent.

This cooling occurs because as air rises, the pressure decreases, allowing the air to expand. As it expands, it loses energy and therefore cools down. The rate of 3 degrees Celsius per 1,000 feet is a general rule for unsaturated air, distinguishing it from the cooling rates associated with saturated air, which is usually higher due to the release of latent heat through condensation.

Understanding this principle is crucial for meteorology and aviation, as it affects weather patterns, cloud formation, and aircraft performance at varying altitudes. The other choices represent rates that are not typical for the cooling of unsaturated air and would thus provide inaccurate information in this context.