Final answer:
The cologne particles spread through the house due to diffusion, where particles move from an area of higher concentration to an area of lower concentration. This allowed the scent of the cologne to be detected in different areas.
Step-by-step explanation:
In order to explain why John was able to smell the cologne throughout the house even though it was in his room, we need to understand the concept of concentration gradient. Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. So, when John sprayed the cologne in his room, the cologne particles started to spread out and move from an area of high concentration (his room) to an area of lower concentration (other parts of the house). This movement of particles allowed the scent of the cologne to be detected in different areas.