Select the correct definition of isotopes ( 2.5 points) (a) two atoms of the same element having different number of neutrons 10 two atoms of the same element having same atomic number but different mass number (c) both (a) and (b) (d) none of the above.

C

Explanation:

(A) is correct. Isotopes are the same element that only differ in number of neutrons.

(B) is also correct. Atomic number (z) is the number of protons an atom has. Atoms of the same element will have the same number of protons.

Mass number (A) is the sum of protons and neutrons in the center. If protons between two atoms are the same but mass number is not, means they have different number of neutrons. They are isotopes.

(C) States that both A and B are correct

(D) None of the above

Option C is correct

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.