The law conservation of mass, because part of the mass can be converted into energy
also, the elements are changing during nuclear reactions, new elements are formed
For group 16 elements, the atomic radii increases down the group as a shell of electron is added on each time.
Honestly, you can look at the notes you took and even look down some things in google to help u solve ur answer
Answer:
Lithium oxide, Li₂O.
Explanation:
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In this case, according to the given amounts, it is possible to write down the chemical reaction as shown below:

Which means that the metallic oxide has the following formula: M₂O. Next, we can set up the following proportional factors according to the chemical reaction:

Thus, we perform the operations in order to obtain:

So we solve for x as shown below:

Whose molar mass corresponds to lithium, and therefore, the metallic oxide is lithium oxide, Li₂O.
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Answer: The given statement is false.
Explanation:
Precipitation reaction is defined as the chemical reaction in which two aqueous solution upon mixing together results in the formation of an insoluble solid.
For example, 
Here AgCl is present in solid state so, it is the precipitate.
But it is not necessarily true that two aqueous solutions will always result in the formation of a precipitate.
For example, 
Hence, we can conclude that the statement precipitation reactions always occur when two aqueous solutions are mixed, is false.