Answer: Option (a) is the correct answer.
Explanation:
A decomposition reaction is defined as a reaction where a compound dissociates into two or more atoms.
For example, 
Whereas a chemical reaction in which two reactants combine together to result in the formation of a compound is known as a synthesis reaction.
For example,
is a synthesis reaction.
Thus, we can conclude that the statement chemical reaction A, because the reactant is a compound identifies the decomposition reaction and describes a substance is involved.
I think it is because it is directly about the north or south pole (I forget) so while all the other stars seem to rotate around because the Earth is rotating but the North Star is directly in the center. Don't take my word though.
<span>According to the law of conservation of mass, the masses of the products and reactants must be the same. Adding calcium to the product side is considered a mistake if it is not in the reactant side of a particular chemical equation because it is impossible to produce calcium from thin air (unless this is a nuclear reaction).</span>
The first choice is correct. K will give up electrons more easily, due to its smaller electronegativity.
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