Is Scrap Metal Pieces an example of a pure substance or a mixture?

In the space, show a correct numerical setup for calculating the number of moles of co2 present in 11 grams of co2

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?

Stoichiometry- i need with 14 and 15! an explanation would be appreciated!