Discovered in the late 1800s and fundamental to important technological advances of the 20th century, silently transmit information all over the world to extend human communications. a) microwaves b) radio waves c) seismic waves d) infrared waves

Radio waves. Microwaves would cook the earth, seismic waves would just cause earthquakes everywhere, and infrared waves would also cook the earth.

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.