The element hydrogen has one valence electron. which of the following elements also has only one valence electron?
a. rubidium
b. helium
c. scandium
d. krypton

Alidded glass container is filled with a colored gas. after a period of time, it is observed that the gas is uniformly spread throughout the box and that the movement has slowed considerably. next, a warm iron plate is carefully placed under the box. why is there resumed movement of the gas in the container?