Number of 4f electrons in given lanthanoid ions

1. A.
   10
2. B.
   12
3. C.
   11
4. D.
   9

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1. A.
   ${Eu}^{2 +}$ and ${Tm}^{2 +}$
2. B.
   ${Sm}^{2 +}$ and ${Tm}^{3 +}$
3. C.
   ${Tb}^{4 +}$ and ${Yb}^{2 +}$
4. D.
   ${Dy}^{3 +}$ and ${Yb}^{3 +}$

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1. A.
   ${Sm}^{2 +}$ and ${Er}^{3 +}$
2. B.
   ${Yb}^{2 +}$ and ${Lu}^{3 +}$
3. C.
   ${Eu}^{2 +}$ and ${Tb}^{4 +}$
4. D.
   ${Tb}^{2 +}$ and ${Tm}^{4 +}$

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1. A.
   $4f^{3}$
2. B.
   $4f^{4}6{\text{ }s}^{2}$
3. C.
   $4f^{4}$
4. D.
   $4f^{2}6s^{2}$

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1. A.
   (A) and (B) only
2. B.
   (A) and (D) only
3. C.
   (B) and (E) only
4. D.
   (B) and (C) only

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