Niobium and tantalum metals are used in making surgical instruments because they are

Assertion : $E^o$ for $Mn^{3+}/Mn^{2+}$ is more positive than $Cr^{3+}/Cr^{2+}$.
Reason : The third ionization energy of $Mn$ is larger than that of $Cr$.

The $E^{\Theta} (M^{2+} / M)$ value for copper is positive $(+0.34 \ V)$. What is the possible reason for this? (Hint: consider its high $\Delta_{a} H^{\Theta}$ and low $\Delta_{hyd} H^{\Theta}$)

Explain briefly how the $+2$ oxidation state becomes more stable in the first half of the first-row transition elements as the atomic number increases.

The atomic number of an element is $26$. The element shows:

Which element of the $3d$-series has the highest third ionisation enthalpy?