Which of the following can not be oxidized?

${\mathrm{NO}}_3^{-}, {\mathrm{CO}}_3^{2-}, {\mathrm{PO}}_4^{3-}$

Explain the following:

(i) Why argon (atomic mass $=39.94$) has been placed before potassium (atomic mass $=39.10$) in the Modern periodic table?

(ii) There are only $15$ lanthanides and only $15$ actinides in Modern periodic table.

Arrange the following in correct order of stability:

(i) ${\mathrm{Ga}}^{+},{\ln }^{+},{\mathrm{Tl}}^{+}$

(ii) ${\mathrm{As}}^{+5},{\mathrm{Sb}}^{+5},{\mathrm{Bi}}^{+5}$