In a sample of ethyl ethanoate $(CH_3COOC_2H_5 )$ the two oxygen atoms have the same number of electrons but different number of neutrons. Which of the following is the correct reason for it?

Question

$\begin{array}{1 1} \text{(a) One of the oxygen atoms has gained electrons} \\ \text{ (b) One of the oxygen atoms has gained two neutrons} \\ \text{(c) The two oxygen atoms are isotopes} \\ \text{ (d) The two oxygen atoms are isobars.} \end{array} $