Which of the following elements does not form an amalgam?

Platinum,palladium,iridium,etc.,are called noble metals because

The metal ion which does not form coloured compounds is

Although $Cr^{3+}$ and $Co^{2+}$ ions have the same number of unpaired electrons,the magnetic moment of $Cr^{3+}$ is $3.87 \ BM$ and that of $Co^{2+}$ is $4.87 \ BM$. Why?

Which of the following may be colourless?

Which element exhibits a $+7$ oxidation state?