Number of protons, neutrons and electrons

Number of protons, neutrons and electrons in the four specimens A, B, C and D are respectively 6, 6, 6 ; 7, 7, 7; 6, 8, 6; and 9, 10, 10. Which of them are
(i) isotopes and
(ii) isobars? Why?

(i) Isotopes are A and C because they have same number of protons (atomic number) but different number of neutrons. .
(ii) Isobars are B and C because they have same mass numbers but different number of protons (atomic number).
Mass number of B = Number of protons + number of neutrons = 7 + 7 = 14
Mass number of C= 6 + 8 = 14