Final answer:
The temperature in the classroom dropped because the air particles in the room transferred kinetic energy to the cooler outside air particles, resulting in the inside air losing energy and the temperature decreasing.
Step-by-step explanation:
The best explanation for why the temperature in the classroom dropped by 5°C when the windows were opened and then closed is b- The air particles in the room transferred kinetic energy to the air particles from outside. When the warmer air inside the room comes into contact with the cooler air from outside, the particles collide, and energy is transferred from the warmer particles to the cooler ones. This process results in the warmer air losing kinetic energy, and therefore, the overall temperature of the room decreases.
When dealing with thermal interactions, it's important to note that heat transfer occurs from the warmer object to the cooler one until thermal equilibrium is reached. Option a is incorrect because cold cannot be added; thermal dynamics is about the transfer of energy. Option c partially explains the process, but it implies an overall energy loss, rather than a redistribution. Option d is incorrect because the outside air particles would not add kinetic energy to the room's air particles in this scenario since the outside air is cooler.