Final answer:
The standard lapse rate is the rate at which temperature decreases with altitude, typically about 6.5°C per kilometer.
Step-by-step explanation:
The standard lapse rate refers to the average rate at which temperature decreases with an increase in altitude in the troposphere, the lowest layer of Earth's atmosphere. This rate is generally about 6.5 degrees Celsius per kilometer. Therefore, the correct answer to what the standard lapse rate is: c) Decrease in temperature with altitude. Option a) refers to a temperature inversion, which is the opposite of the normal lapse rate phenomenon, and d) suggests an increase in temperature with altitude, which is also incorrect regarding the standard lapse rate. Option b) adiabatic change, deals with the temperature change of a gas or air parcel without the exchange of heat with its surroundings, which is related but distinct from the lapse rate concept.