Answer:
A. the atomic number
Explanation:
It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth.
Answer:
It takes 1.9 
years to distribute all the grains.
Explanation:
In one second, 
grains of wheat are distributed.
We are supposed to find the time it would take to Distribute Avogadro number of grains.
1 avogadro number = 6.022 
Number of grains distributed in 1 day = 86400 
= 8.64 
Number of grains distributed in 1 year= 8.64 
= 3.1536 
Time taken = 
= 
= 1.9
Pure substances are substances<span> that are made of only one type of atom or molecule....</span>
Answer:
Explanation:
A chemical property describes the ability of a substance to undergo a specific chemical change.
A chemical reaction is a process that occurs when one or more substances are changed into one or more new substances.
Differences
Chemical properties are properties that can be observed or measured when a substance undergoes a chemical change.
Physical properties are properties that can be observed without bringing a chemical change.
Another one
chemical properties; can be used to predict how substances react.
chemical changes; It is mostly used in identifying or describing the substance.
I have a feeling that #2 is the one.
