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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3df219

Atomic numbers: Th 90 ( $6 d^{2} 7 s^{2}$ ), Pa 91 ( $5 f^{2} 6 d^{1} 7 s^{2}$ ), U 92 ( $5 f^{3} 6 d^{1} 7 s^{2}$ ), Np 93 ( $5 f^{4} 6 d^{1} 7 s^{2}$ ), Pu 94 ( $5 f^{6} 7 s^{2}$ ). Which species have no $5 f$ electron?

A $Pu X^{6 +}$
B $Pa X^{5 +}$
C $Th X^{4 +}$
D $Np X^{7 +}$

Answer: B, C, D

Pa X^{5 +}

removes all five valence electrons (including

5 f^{2}

) and

Np X^{7 +}

removes all seven;

Th X^{4 +}

removes

6 d^{2}

and

7 s^{2}

.

Pu X^{6 +}

loses only

7 s^{2}

and four

5 f

electrons, leaving

5 f^{2}

.

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