Question

Which of the following is not correct about the 3d and 4f series elements?

• A. 3d elements show more oxidation states than 4f series elements
• B. The energy difference between 3d and 4s orbital is very low
• C. Eu (II) is more stable than Ce (II)
• D. The paramagnetic character in 3d series elements increases from $Sc$ to $Cu$

Answer 1

The correct option is D The paramagnetic character in 3d series elements increases from $Sc$ to $Cu$

a) 3d elements show variable valency as these elements use both 3d and 4s electrons. The 4f series elements generally show +3 oxidation state only.
b) The energy difference between 3d and 4s orbital is very little.
c) The electronic configuration of
$Ce=\left[Xe\right]4f^{1}5d^{1}6s^2$
$Eu=\left[Xe\right]4f^{7}6s^2$
Thus in +2 state Eu attains a stable half filled configuration. Hence Eu (II) is more stable than Ce (II).
d) Paramagnetic character depends on the number of unpaired electrons. From the electronic configuration, $Mn$ has the highest number of unpaired electrons, so paramagnetism increases till $Mn$ and then decreases.