- A$Ce^{+4},\, Yb^{+2}$
- ✓$Gd^{+3},\, Nd^{+3}$
- C$La^{+3}, \,Lu^{+3}$
- D$Lr^{+3}, \,Lu^{+3}$
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$R - X \rightarrow R ^{\oplus} X ^{\ominus} \rightarrow R ^{\oplus} \| X ^{\ominus} \stackrel{ Y^\ominus }{\rightarrow} R - Y + X ^{\ominus}$
Ion pair Solvent separated ion pair
A student writes general characteristics based on the given mechanism as:
$(a)$ The reaction is favoured by weak nucleophiles
$(b)$ $R^ \oplus$ would be easily formed if the substituents are bulky
$(c)$ The reaction is accompained by recemization
$(d)$ The reaction is favoured by non-polar solvents.
Which observations are correct $?$
Set $1$: $Al_2O_3 .xH_2O\, (s)$ and $OH^-(aq)$
Set $2$: $Al_2O_3 .xH_2O\, (s)$ and $H_2O\,(l)$
Set $3$: $Al_2O_3 .xH_2O\, (s)$ and $H^+(aq)$
Set $4$: $Al_2O_3 .xH_2O\, (s)$ and $NH_3(aq)$

Assertion $(A)$ : The first ionization enthalpy of $3 d$ series elements is more than that of group $2$ metals
Reason $(R)$ : In $3d$ series of elements successive filling of d-orbitals takes place.
In the light of the above statements, choose the correct answer from the options given below :
