“a point at which rays of light, heat, or other radiation meet after being refracted or reflected.” Meaning multiple light rays or heat (and other forms of radiation) are all being refracted or reflecting to a certain point
Ohh this is quite a lot umm i’ll be back hold on
On mars people would way less.
An example of this is that if I weighed 700 pounds (I don't by the way) I would then weigh 500 pounds or less.

Each increase in the prefix is a division by 1000.
The answer of a & b are force of cohesion and force of adhesion
Of rest two answers I don't know