According to Lewis concept, the trend in the relative basic strengths of \(\rm ClO_4^-, ClO_3^-, ClO_2^-\)is: 

CONCEPT:

Lewis Basic Strength

• According to the Lewis concept, a base is a species that can donate an electron pair.
• In oxyanions of chlorine (ClO^-, ClO₂^-, ClO₃^-, ClO₄^-), the basicity depends on the electron density available on the oxygen atoms.
• As the oxidation number of chlorine increases, it pulls electron density towards itself due to increased electronegativity (inductive effect).
• This reduces the availability of electron density on oxygen atoms for donation, decreasing Lewis basic strength.

EXPLANATION:

• Oxidation states of chlorine in the given ions are:
  • ClO₂^-: +3
  • ClO₃^-: +5
  • ClO₄^-: +7
• Higher oxidation state increases the electron-withdrawing power of chlorine, which reduces the electron density on the ion.
• Hence, ClO₂^- has the highest basic strength, followed by ClO₃^-, and then ClO₄^-.

Therefore, the correct order of Lewis basic strength is ClO₂^- > ClO₃^- > ClO₄^-