Which of the following types of metals form the most effective catalysts?

The correct order of $E^o$ $M^{2+}/M$ values with negative sign for the four successive elements $Cr$,$Mn$,$Fe$ and $Co$ is

The hardness of interstitial compounds is comparable to which of the following?

Although Zirconium belongs to the $4d$ transition series and Hafnium to the $5d$ transition series,they show similar physical and chemical properties because . . . . . . .

Which of the following metal ions in their respective oxidation states forms a coloured compound?

The $I.P.$ values of $Cr, Zn, Mn$,and $Hg$ are $7.4 \ eV, 6.7 \ eV, 10.4 \ eV$,and $9.3 \ eV$. These $I.P.$ values are not listed in the order of the elements. Identify the correct $I.P.$ value for the given elements.