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Question

Chemistry Question on d -and f -Block Elements

Which of the following compound, on reaction with NaOHNaOH and Na2O2Na _{2} O _{2}, gives yellow colour?

A

Zn(OH)2Zn ( OH )_{2}

B

Al(OH)3Al ( OH )_{3}

C

Cr(OH)3Cr ( OH )_{3}

D

CaCO3CaCO _{3}

Answer

Cr(OH)3Cr ( OH )_{3}

Explanation

Solution

Yellow colour is due to the formation of CrO42CrO _{4}^{2-} ion. Cr(OH)3+NaOH+Na2O2Na2CrO4+2H2OCr ( OH )_{3}+ NaOH + Na _{2} O _{2} \rightarrow Na _{2} CrO _{4}+2 H _{2} O