Question
The electronic configurations of $$Eu$$ ( Atomic no. 63 ), $$Gd$$ ( Atomic no. 64 ) and $$Tb$$ ( Atomic no. 65 ) are
A.
$$\left[ {Xe} \right]4{f^6}5{d^1}6{s^2},\left[ {Xe} \right]4{f^7}5{d^1}6{s^2}$$ and $$\left[ {Xe} \right]4{f^9}6{s^2}$$
B.
$$\left[ {Xe} \right]4{f^6}5{d^1}6{s^2},\left[ {Xe} \right]4{f^7}5{d^1}6{s^2}$$ and $$\left[ {Xe} \right]4{f^8}5{d^1}6{s^2}$$
C.
$$\left[ {Xe} \right]4{f^7}6{s^2},\left[ {Xe} \right]4{f^7}5{d^1}6{s^2}$$ and $$\left[ {Xe} \right]4{f^9}6{s^2}$$
D.
$$\left[ {Xe} \right]4{f^7}6{s^2},\left[ {Xe} \right]4{f^8}6{s^2}$$ and $$\left[ {Xe} \right]4{f^8}5{d^1}6{s^2}$$
Answer :
$$\left[ {Xe} \right]4{f^7}6{s^2},\left[ {Xe} \right]4{f^7}5{d^1}6{s^2}$$ and $$\left[ {Xe} \right]4{f^9}6{s^2}$$
Solution :
Electronic configuration of $${}_{63}Eu = {\left[ {Xe} \right]_{54}}4{f^7}6{s^2}$$ Electronic configuration of $${}_{64}Gd = {\left[ {Xe} \right]_{54}}4{f^7}5{d^1}6{s^2}$$
Electronic configuration of $${}_{65}Tb = {\left[ {Xe} \right]_{54}}4{f^9}6{s^2}$$