Physical property of gas:
There are a lot, here are some examples:
=> Air
=> Oxygen
=> Carbon dioxide
=> Flourine
=> Phosphine
=> Argon
=> Carbon monoxide
This examples are all gases and each of these gases has its own physical property. The only thing that they makes them the same are that, they are gas with lesser molecules. Usually gas density is lesser compare to the solid or liquid and most gases has undefined melting point.
Activation energy is defined as the least amount of energy that is needed to be available in a chemical system with potential reactants in order to result a chemical reaction. Therefore, the correct answer would be the first option: the heat released in a reaction.
Answer: Hydrogen molecules will have greatest average speed.
Explanation:
The formula for average speed is :

R = gas constant
T = temperature
M = Molecular Mass
Now putting all the values:



Thus average speed of hydrogen is 8 times the average speed of oxygen. Thus hydrogen molecules will have greatest average speed
The reactivity of metals increases as you move left in a period and as you move down in a group, so Marie needs to know the period and group of the element inside each box. Boxes that show locations in groups 1 or 2 or in period 8 contain the most reactive elements.