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JEE Advanced levelSingle correct optionDifficulty 3 of 3sb152

A sample of $2.5 g$ of $BeO$ (molar mass $25 g mo l^{- 1}$ ) is dissolved completely in excess aqueous NaOH to form $Na X_{2} [Be (OH) X_{4}]$ . The mass of NaOH ( $40 g mo l^{- 1}$ ) consumed is:

A $4.0 g$
B $8.0 g$
C $12.0 g$
D $16.0 g$

Answer: B

BeO + 2 NaOH + H X_{2} O Na X_{2} [Be (OH) X_{4}]

is the amphoteric reaction, which uses 2 mol NaOH per mol BeO. Moles of BeO

= 2.5/25 = 0.1

, so NaOH

= 0.2

mol

= 0.2 \times 40 = 8.0

g.

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