Q. Which of the following is colored compound?
Bihar CECEBihar CECE 2005Coordination Compounds
Solution:
The d block elements form coloured compounds. These compounds have ions with unpaired electron in d- subshell.
(i) Na and Mg belong to s-block, so $NaCl$ and $MgCl _{2}$ are colourless compounds.
(ii) $CuF _{2}$ oxidation state of $Cu$ in $Cu F _{2}$ is $+2$
$Cu ^{2+},=1 s^{2}, 2 s^{2}, 2 p^{6}, 3 s^{2}, 3 p^{6}, 4 s^{0}, 3 d^{9}$
$\therefore $ CuF $_{2}$ in which Cu has one unpaired electron is coloured.
(iii) CuI Oxidation state of $Cu$ in CuI $=+1$
$Cu ^{+}-1 s^{2}, 2 s^{2}, 2 p^{6}, 3 s^{2}, 3 p^{6}, 4 s^{0}, 3 d^{10}$
It has no unpaired electron. So CuI is colourless.
$\therefore $ Only $CuF _{2}$ is coloured among given choices.
