I think it is B, because the sun’s size is pretty average
A thermogram<span> enables the human eye to "see" light in the infrared range of the electromagnetic spectrum.</span>
Yes, it is diffusion !
Diffusion is the process in which gas, through random movement of particles, tends to fill up the whole volume of the container in which it is placed. So a similar process would lead the smoke, which is in form of gas (or light particles), to fill in the whole room in which it is contained.