I think the answer is:
B. Chemical Change.
What Can you be more clear --Molecules change it from being less dense
Answer: Originally viewed as a single event, the Taconic orogeny is now known to consist of at least three episodes. The first took place in the Early Ordovician Epoch near Maine and Newfoundland. The second was centred on eastern Tennessee in the Middle Ordovician Epoch.
Answer: Activation energy
Explanation:
In a chemical reaction, the reactants contains particles which must collide in order for a reaction to occur. The rate of reaction depends on the frequency of effective collision between the reacting particles. Effective collision are those that result in reactions, which when they occur the colliding particles become activated with increased kinetic energy.
This energy must exceed a particular energy barrier for a particular reaction if the reaction must take place. This energy barrier that must be overcome before a reaction takes place is known as the ACTIVATION ENERGY.
To explain further, when two particles or molecules A and B come in contact with each other, for a reaction to take place, they must collide with a sufficient force to break the bond that exists between them. The minimum combined kinetic energy these reactant particles must possess in order for their collision to result in a reaction is called the activation energy.
fourth period
The third period is similar to the second, except the 3s and 3p sublevels are being filled. Because the 3d sublevel does not fill until after the 4s sublevel, the fourth period contains 18 elements, due to the 10 additional electrons that can be accommodated by the 3d orbitals.
