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JEE Main levelSingle correct optionDifficulty 2 of 3df178

Aqueous $Eu X^{2 +}$ ( $4 f^{7}$ ) slowly reduces $H X^{+}$ in dilute acid. The balanced ionic equation with the product in its characteristic state is

A $Eu X^{2 +} + 2 H X^{+} Eu X^{4 +} + H X_{2}$
B $2 Eu X^{2 +} + 2 H X^{+} 2 Eu X^{+} + H X_{2}$
C $2 Eu X^{2 +} + 2 H X^{+} 2 Eu X^{3 +} + H X_{2}$
D $Eu X^{2 +} + H X^{+} Eu X^{3 +} + H X_{2}$

Answer: C

Europium(II) is oxidised to the characteristic

Eu X^{3 +}

(

4 f^{6}

) while

H X^{+}

is reduced to

H X_{2}

. Charge balance:

2 (+ 2) + 2 (+ 1) = + 6 = 2 (+ 3)

, and the atoms balance. The other options are unbalanced in charge or give the non-existent

Eu X^{+}

or

Eu X^{4 +}

product.

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