A brief information about two atoms $X$ and $Y$ is given:
$X:$ Atomic number $=7$, Mass number $=14$
$Y:$ Atomic number $=7$, Mass number $=15$
Which of the following is correct about these two atoms?

Which of the following are isobars?

Which of the following statements are correct regarding the elements given below?

${}_{19}{}^{39} \mathrm{K}, {}_{53}{}^{127}\mathrm{I}, {}_{17}{}^{35}\mathrm{Cl}, {}_{35}{}^{80}\mathrm{Br}, {}_{18}{}^{40}\mathrm{Ar}$

I The correct order of increasing proton number is $\mathrm{K}<\mathrm{Cl}<\mathrm{Br}<\mathrm{I}<\mathrm{Ar}$
II The correct order of increasing mass number is $\mathrm{Cl}<\mathrm{K}<\mathrm{Ar}<\mathrm{Br}<\mathrm{I}$
III There is difference in the orders of proton number and mass number.
IV The number of protons is equal to number of neutrons in all the given elements.

Identify the difference between particles of each given pair.

(I)  ${}^6\mathrm{Li}$ and ${}^7\mathrm{Li}$
(II)  ${}^{32} \mathrm{S}$ and ${{}^{32} \mathrm{S}}^{2-}$
(III)  ${{}^{39} \mathrm{K}}^{+}$ and ${{}^{40}\mathrm{Ca}}^{2+}$