Could be easy for some people and hard for some people.
Answer;
At the top of group 17
Explanation;
Reactivity in chemistry deals with whether something will react with another substance. The reactivity of an element can be predicted based on its location on the periodic table.
The most reactive nonmetal is fluorine. Fluorine is a halogen, which is Group 17 on the periodic table, and the halogens are the most reactive nonmetals. This is because they all have one empty space in their valence electron shells. Of the halogens, fluorine's empty space is closest to the positively charged nucleus. This means it pulls harder on another atom's electrons to fill that empty space.
The collision of car 2 is more violent (because more impulse is exerted)
Explanation:
The collision which is more violent is the one in which more impulse is exchanged.
The impulse exerted by each car on the wall is equal to the change in momentum of the car:

where
m is the mass of the car
is the change in velocity
For the car 1,
m = 1000 kg
(the sign is negative because the velocity of the car has changed from 100 km/h to 0 km/h)
So the magnitude of the impulse of car 1 is

For the car 2,
m = 1200 kg

So the magnitude of the impulse of car 2 is

So, car 2 exerts a larger impulse, therefore its impact is more violent.
Learn more about impulse and change in momentum:
brainly.com/question/9484203
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Salutations!
What is the smallest unit of a substance that keeps all of the physical and chemical properties of that substance?
Molecules is the smallest unit of a substance that keeps all of the physical and chemical properties of that substance. It is a group of atoms bounded together, and it can participate in a chemical reaction/
Hope I helped (:
Have a great day!