Q42 / 180 · KCET 2014 · Chemistry

For the properties mentioned, the correct trend for the different species is in

  • A
    inert pair effect \( -A l>G a>I n \)
  • B
    first ionization enthalpy \( -B>A l>T l \)
  • Correct answer
    C
    strength as Lewis acid - \( \mathrm{BCl}_{3}>\mathrm{AlCl}_{3}>\mathrm{GaCl}_{3} \)
  • D
    oxidizing property \( -A l^{3+}>I n^{3+}>T l^{3+} \)

Solution

Lewis acid strength decreases down the group therefore, order is $\mathrm{BCl}_{3}>\mathrm{Al} \mathrm{Cl}_{3}>\mathrm{GaCl}_{3}$ First ionization energy for Group 13 elements decreases down the group till Al then increases for Ga due to d-electron contraction, decrease for In then again increases for TI due to lanthanoid contraction, that is, B $>\mathrm{Tl}>\mathrm{Ga}>\mathrm{Al}>\mathrm{In}$. Inert pair effect shown by heavier elements only, therefore, for $\mathrm{Tl}$, $+1$ oxidation states in more stable and it strong oxidizing agent in $+3$ states.

Hence, the correct answer is option: 'C'.

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