The transition element that has lowest enthalpy of atomisation is

The melting point of $Zn$ is lower as compared to those of the other elements of $3d$ series because

$(a)$ Transition metals can act as catalysts because these can change their oxidation state. How does $Fe(III)$ catalyse the reaction between iodide and persulphate ions ?

$(b)$ Mention any three processes where transition metals act as catalysts.

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

Consider the following reaction

$\mathrm{MnO}_2+\mathrm{KOH}+\mathrm{O}_2 \rightarrow \mathrm{A}+\mathrm{H}_2 \mathrm{O} .$

Product ' $A$ ' in neutral or acidic medium disproportionate to give products ' $\mathrm{B}$ ' and ' $\mathrm{C}$ ' along with water. The sum of spin-only magnetic moment values of $B$ and $C$ is . . . . . .$BM$. (nearest integer)

(Given atomic number of $\mathrm{Mn}$ is $25$ )

Which of the following pair of elements cannot form an alloy