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<span>The question says.'which option describes a similarity between isotopes of an element. The correct option is C. Isotopes have the same number of atomic number but different mass number. The mass number is the summation of proton and neutron. The number of proton is always constant but that of neutron changes to reflect the existence of isotopes.</span>
Answer: Option A) the total energy of the universe is constant.
Explanation:
The first law of thermodynamics is also known as the law of conservation of mass.
And it states that matter is neither created nor destroyed during a chemical reaction but changes from one form to another.
Thus, the total energy of the universe is constant (neither created nor destroyed).