Which of the following pair(s) of nucleides is/are isodiaphers?

The correct option is C ${}_6^{12}Cand{}_8^{16}O$
Isodiaphers are the species with different atomic numbers and mass numbers, but with the same number of neutrons in excess.
Number of neutrons in ${}_6^{12}C$= 12 – 6 = 6. Number of protons = 6, (n - p) = 0
Number of neutrons in ${}_8^{16}O$ = 16 – 8 = 8, number of protons = 8, (n - p) = 0
${}_6^{12}Cand{}_8^{16}$O have different atomic numbers and different mass numbers, but the difference between neutrons and protons is same i.e. (n-p)