"A chemistry student attempted to make a 0.2000 M solution of NaCl using a 100.0 mL volumetric flask. She added exactly 100.0 mL of water to the flask, then added 0.02000 mol of NaCl, and found that the total volume in the flask was above the 100.0 mL mark. What was the concentration of the solution?"

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?