What type of electromagnetic wave is used in security pens?

a. x-rays
b. visible light
c. microwaves
d. ultraviolet radiation

Ultra violet radiation

Explanation:  Sun is the major source of these radiations. Ultraviolet  Radiation has the range of 10nm-400nm and are responsible to make the things or spots glow which cannot be seen with the naked eye. These pens are usually fluorescent but are transparent which cn only be seen under the radiation.

This the reason why ultra violet radiations are used for security purposes and to prevent any illegal cause.

the molecules move in straight line until they collide with each other or with the walls of the container. collisions are perfectly elastic; when two molecules collide, they change their directions and kinetic energies, but the total kinetic energy is conserved.

explanation:

the electrical  conductivity  of asolution  of an electrolyte is measured by determining the resistance of thesolution  between two flat or cylindrical electrodes separated by a fixed distance.