Question
The correct statements among the following are,
A. $Mo(VI)$ and $W(VI)$ are less stable than $Cr(VI)$.
B. ${Ce}^{4 +}$ and ${Tb}^{4 +}$ are oxidant while ${Eu}^{2 +}$ and ${Yb}^{2 +}$ are reductant.
C. Cm and Am have seven unpaired electrons.
D. Actinoid contraction is greater from element to element than lanthanoid contraction.
Choose the correct answer from the options given below :
(1) A and B Only
(2) C and D Only
(3) B and D Only
(4) A and C Only
Solution
Sol. [Key Concept: Check each: Mo(VI)/W(VI) are more stable than Cr(VI); Ce$4 +$/Tb$4 +$ oxidise while Eu$2 +$/Yb$2 +$ reduce (B) and actinoid contraction $>$ lanthanoid (D).]
(A) $Mo(VI)$ & $W(VI)$ more stable than $Cr(VI)$
(B) In lanthanoids +3 oxidation state is more stable hance +4 ions act as oxidising agents and +2 ions act as reducing agents.
(C) $Cm - \lbrack Rn\rbrack 5f^{7}6{\text{ }d}^{1}7{\text{ }S}^{2} = 8$ unpaired electrons
$Am - \lbrack Rn\rbrack 5f^{7}6{\text{ }S}^{2} = 7$ unpaired electrons
(D) Actinoid contraction is more than lanthanoid contraction
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