Question

Which of the following statements are incorrect?

• A. Anhydrous $CuSO_4$ is blue in colour
• B. Ruby is $Al_2O_3$ containing about 0.5-1% $Cr^{3+}$ ions
• C. $[Ni(H_2O)_6]^{2+}$ is violet in colour
• D. Vitamin $B_{12}$ is a coordination compound of magnesium

Answer 1

Answer: (A), (C), (D)

Anhydrous $CuSO_4$ is blue in colour, $[Ni(H_2O)_6]^{2+}$ is violet in colour, Vitamin $B_{12}$ is a coordination compound of magnesium

Answer 2

1. Anhydrous $CuSO_4$ is white. The blue colour is characteristic of hydrated copper(II) sulfate ($CuSO_4 \cdot 5H_2O$). Therefore, the statement "Anhydrous $CuSO_4$ is blue in colour" is incorrect.
2. Ruby is $Al_2O_3$ containing about 0.5-1% $Cr^{3+}$ ions. This statement is correct. Ruby is a variety of aluminum oxide (corundum) coloured red by trace amounts of chromium(III) ions.
3. $[Ni(H_2O)_6]^{2+}$ is green in colour. The hexaaquanickel(II) ion is green due to d-d transitions of $Ni^{2+}$ ions. Therefore, the statement "$[Ni(H_2O)_6]^{2+}$ is violet in colour" is incorrect.
4. Vitamin $B_{12}$ is a coordination compound of cobalt. Vitamin $B_{12}$, also known as cobalamin, contains cobalt (Co) as its central metal atom, not magnesium (Mg). Magnesium is the central metal in chlorophyll. Therefore, the statement "Vitamin $B_{12}$ is a coordination compound of magnesium" is incorrect.