Which of the following statement is correct regarding 3d-series of elements ?
(1) Sc has the lowest while Zn has the highest first ionization enthlpy.
(2) Cu has the highest while Sc has the lowest second ionization enthalpy
(3) Zn has the highest third ionization enthalpy
(4) Fe has lower third ionization enthalpy relative to Mn

Options

A. (i), (ii), (iii)
B. (ii), (iii)
C. (i), (ii), (iii), (iv)
D. (i), (iv)

Answer

C

Explanation

In the case of d-block metals, the variation of ionization enthalpy across the periods and down the groups parallel quite closely the trend in atomic size. As we move across a period, the effective nuclear charge experienced by ns electrons goes on increasing causing the shells to shrink in size and thus making it difficult to removed the electrons. Thus along a period the ionization enthalpy generally increases. The second and third ionization enthalpies follow the same pattern, except for the second ionization enthalpies of Cr and Cu which are comparatively higher due to extra ionization enthalpies of Mn and Zn are comparatively higher due to extra stability of `3d^(5)` and `3d^(10)` configuration. Similarly the third ionization enthalpies of Mn and Zn are comparatively higher due to extra stability of `3d^(5)` and `3d^(10)` configuration. As the decrease in the size of atoms of the d-block metals is less than that of the main group elements along a period, the ionization enthalpies to the increase along the series only slightly as compared to the main group elements. For example, in 3d-series the elements Ti, V and Cr have similar first ionization enthalpies. Similarly the elements Fe, Co, Ni and Cu have similar first ionization enthalpies. Since (n-1) d and ns electrons do not differ much in energy, the difference in the successive ionization enthalpies is relatively small. As we move down a group form the elements of first d series to those of the second d series, there is a decrease in the ionization enthalpy on account of increasing size. But it again increases when we move further down the group from second to the third d-series. This trend is consistent with relatively small size of the atoms of elements of the third d series due to the insertion of the lanthanides which causes the third row d-block elements to have grater than expected effective nuclear charge.