This is a chemical reaction.
Atoms are electrically neutral because the number of protons, which carry a 1+ charge, in the nucleus of an atom is equal to the number of electrons, which carry a 1- charge, in the atom. The result is that the total positive charge of the protons cancels out the total negative charge of the electrons so that the net charge of the atom is zero. Most atoms, however, can either gain or lose electrons; when they do so, the number of electrons becomes different from the number of protons in the nucleus. The resulting charged species is called an ion.
The correct reference for this isotope is A. Oxygen-18.
The conjugate base of ch3ch2co2h or propanoic acid would be CH3CH2COO- or propanoate. The conjugate base is what is left after an acid has donated a proton in a reaction. Hope this answers the question. Have a nice day.