Which of the following compounds is coloured?

State the reason for the stability of the $Gd^{3+}$ ion.

The catalytic activity of transition metals and their compounds is due to their

Which of the following statements are correct about $Zn, Cd$ and $Hg$?
$A$. They exhibit high enthalpy of atomization as the d-subshell is full.
$B$. $Zn$ and $Cd$ do not show variable oxidation state while $Hg$ shows $+I$ and $+II$.
$C$. Compounds of $Zn, Cd$ and $Hg$ are paramagnetic in nature.
$D$. $Zn, Cd$ and $Hg$ are called soft metals.
Choose the most appropriate from the options given below:

Which of the following compounds is expected to be colourless?

Which pair of ions is colourless?