Which of the following will not act as oxidising agents?
Although +3 is the characteristic oxidation state for lanthanoids but cerium also shows +4 oxidation state because
Why does copper not replace hydrogen from acids?
Copper not replace hydrogen from acids because Cu has positive $E^{\circ}$ value, i.e., less reactive than hydrogen which has electrode potential 0.00 V .
Why $\mathrm{E}^{-}$values for $\mathrm{Mn}, \mathrm{Ni}$ and Zn are more negative than expected?
Negative values of $\mathrm{Mn}^{2+}$ and $\mathrm{Zn}^{2+}$ are related to stabilities of half-filled and completely filled configuration respectively. But for $\mathrm{Ni}^{2+}, E^{\circ}$ value is related to the highest negative enthalpy of hydration. Hence, $E^{\mathrm{S}}$ values for $\mathrm{Mn}, \mathrm{Ni}$ and Zn are more negative than expected.
Why first ionisation enthalpy of Cr is lower than that of Zn ?
Ionisation enthalpy of Cr is less than that of Zn because Cr has stable $d^5$ configuration. In case of zinc, electron comes out from completely filled $4 s$-orbital. So, removal of electron from zinc requires more energy as compared to the chromium.