Arrange the following elements in order of increasing (from smallest to largest) atomic size: K, O, Cs, Se. Explain the reasoning behind your chosen order. Do not simply restate the trend, but rather explain why the trend exists.

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?