Answer:
there are elemental molecules, made from one type of atom (pure), example: oxygen and there are compound molecules, made from more then one type of atom, for example carbon dioxide
Answer:
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air.
Explanation:
Answer : The correct answer is " System ".
A group of things or part that form a whole is known as system .
Or System can be defined as a interacting or interdependent group of items that is forming a unified whole . For example : Gravitational system , thermodynamic system . These both systems have interacting bodies which influenced by some force .
Or it can be said : A group of parts that are combined to form whole which works a complete unit . For example : computers , telephones etc .
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