Activated charcoal is used in gas
masks. what physical property is
related to this use?

Answer:

physical property is  related to the use of Activated charcoal  in gas  masks is  Physical adsorption

Explanation:

Respirators in the gas masks has a 2-stage inhalation protection process . In the first step, particle filter is used that behaves like a physical barrier that removes bacteria from air which is inhaled. When the bacteria is inhaled, it gets entangled in the filter fibres preventing it from being inhaled into the lungs.

In the next stage , activated charcoal is used .This layer with highly porous charcoal attracts and binds to toxins. Through adsorption process, a solid or a liquid can trap particles on its surface. Toxins that pass through the charcoal become bonded to its surface, preventing inhalation of the toxins.  

there is none because earth is stationary and flat.