How can we realize that light travel in straight line ?​

In a hydrogen molecule there are a total of four charges, 2 protons in the two nuclei, and 2 electrons. how many unique charge-pairs are there (without double counting)?

Energy can be transformed from one form to another. the diagram shows one such process. which energy transformation is represented in the diagram? nuclear to thermal and radiant nuclear to electrical and chemical chemical to nuclear and radiant chemical to electrical and nuclear

What happens to the vapor pressure of a substance when its surface area is increased at constant temperature?