How does installing a cool roof help save energy? A. By encouraging people to spend time on the roof, less energy needs to be used for cooling the building.
OB By absorbing sunlight, the building no longer needs to rely on a heating system.
C. By keeping air conditioner units on the rooftop, less runoff heat is captured by the building in the cooling process.
D. By reflecting the sun's light, the building's cooling systems have less work to do.

D. By reflecting the sun's light, the building's cooling systems have less work to do

A reflective roof can help keep a house cooler when the hot sun beats on it, but it will not lower a home’s heating bill, and may even slightly raise it. It makes sense to install a cool roof, which reflects heat but does not absorb it, only where the summers are extremely hot or humid. Most residential cool roofs are in southern and southwestern states, although homes where the summer air is especially humid—in cities like New York, Washington, or Indianapolis, for instance—also are candidates. Still, the Cool Roof Rating Council (CRRC) says cool roof owners may pay slightly more to heat their homes, although the summer savings outpace the increased heating bill.

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.