JEE Main · 2020 · 09 Jan 2020 · Shift 1 · d and f Block Elements

The electronic configurations of bivalent europium and trivalent cerium are: (atomic number:

Xe = 54, Ce = 58, Eu = 63

)

Answer: (B)

Solution

Europium,

[Xe] 4 f^{7} 6 s^{2}

, loses its two

6 s

electrons to become

E u^{2 +} = [Xe] 4 f^{7}

, a configuration made especially stable by the half-filled

f

subshell. Cerium,

[Xe] 4 f^{1} 5 d^{1} 6 s^{2}

, loses three electrons to become

C e^{3 +} = [Xe] 4 f^{1}

JEE Main · 2020 · 09 Jan 2020 · Shift 1 · Single correct option