You look at the atomic mass.. The number of neutrons is different for different individual atoms of the same element, each atom is also known an isotope. Looking at a periodic table, the atomic mass listed is the average atomic mass for all isotopes of that element found in nature.
I think it is B the distance light travels from the sun to the earth
There are 7 periods in the modern periodic table
Answer:

Explanation:
Hello,
In this case, the by mass percent is computed as shown below:

Whereas the solute is the sugar and the solvent the water, therefore, the concentration results:

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Answer: What type of chemical reaction is rusting of iron?
Rust is formed when iron reacts with oxygen in moist air. The following chemical equation represents the reaction: 4Fe + 3O2 → 2Fe2O3. Water is necessary for the oxidation reaction to occur and to facilitate transport of the electrons.