An isomer is molecule with the same atoms as other but with a different distribution (position, optic, spacial, geometrical, etc).
This applies to molecules and not to atoms. (options A and B can't be)
The isotopes are two atoms of the same element (equal proton number) but with different mass number. This is the case of I-131 and I-133. SO option C is correct.
Also, I-131/Xe-131 and I-133/Cs-133 are two pairs of isobars (two atoms of different elements with the same mass number).
Isotopes are two atoms with the same number of protons, but a different number of neutrons. Because they have the same number of proton they are atoms of the same element, but with different masses. so, the answer is c. i hope this will help you
Explanation: Because the operation is subtraction, you would count the number of digits after the decimal point. Then you would perform the operation and round your answer to the SMALLER number of digits after the decimal point.
