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JEE Main levelSingle correct optionDifficulty 2 of 3df184

Lanthanoid metals react with hot water. The balanced equation, with the metal in its characteristic oxidation state, is

A $La + 3 H X_{2} O La (OH) X_{3} + 3 H X_{2}$
B $2 La + 6 H X_{2} O 2 La (OH) X_{3} + 3 H X_{2}$
C $La + 2 H X_{2} O La (OH) X_{2} + H X_{2}$
D $4 La + 6 H X_{2} O 4 La (OH) X_{3} + 3 H X_{2}$

Answer: B

The lanthanoid is oxidised to

La X^{3 +}

(as the hydroxide) and water is reduced to

H X_{2}

. Balance: 2 La, 12 H and 6 O on both sides in the first option. The second gives the unstable

+ 2

state, and the last two are not balanced in hydrogen.

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