Elements are substances that contain only 1 kind of atom.
Explanation:
A chemical reaction is defined as the reaction in which bonds between the reactants either break or form which leads to the formation of a new substance.
For example, 
So, when we drop a sodium metal into water then it produces a frizzing sound which shows the metal is reacting with water.
We know that when two aqueous solutions chemically react with each other then it may lead to the formation of an insoluble substance which is known as precipitate.
This means that formation of a precipitate is also a chemical reaction.
Thus, we can conclude that following are the statements which show evidence for a chemical reaction.
- Dropping sodium metal into water produces fizzing.
- Mixing two aqueous solutions produces a precipitate.
Answer:
(See explanation for further details)
Explanation:
1) The quantity of moles of sulfur is:


2) The number of atoms of helium is:


3) The quantity of moles of carbon monoxide is:


4) The number of molecules of sulfur dioxide is:


5) The quantity of moles of sodium chloride is:


6) The number of formula units of magnesium iodide is:


7) The quantity of moles of potassium permanganate is:


8) The number of molecules of carbon tetrachloride is:


9) The quantity of moles of aluminium is:


10) The number of molecules of oxygen difluoride is:

