Question

Account for: a) Highest fluoride of ${\text{Mn}}$ is ${\text{Mn}}{{\text{F}}_4}$ whereas the highest oxide is ${\text{M}}{{\text{n}}_2}{{\text{O}}_7}$.
b) Transition metals and their compounds show catalytic property.

Answer 1

We know that fluorine is the most electronegative element of the periodic table. All the halogens belong to group number $17$. It is also called the halogen family.
We know that transition metals belong to the d block of the periodic table.

Complete answer:
a) We know that the member of group $16$, that is oxygen, has a great tendency to form more stable oxide of manganese. Higher the oxidation state of the manganese atom, the more stable the oxide is. Oxygen can stabilize the compound by forming multiple bonds as compared to fluorine. Fluorine is the first member of the halogen family. Fluorine does not have the ability to form multiple bonds. Thus, the compound of fluorine with manganese in its highest oxidation state is ${\text{Mn}}{{\text{F}}_4}$.
b) Generally, transition metals are present in the d block of the periodic table. But all the d block elements are not transition metals. Transition metals are those in which an element in its common oxidation state contains unpaired electrons. The main character of transition metal is the presence of unpaired electrons in its most common oxidation state.
Transition metals are able to act as catalysts, due to their ability to show variable oxidation states and ability to form complexes.

Additional information:
Other halogens like chlorine, bromine, iodine except for fluorine are able to show variable oxidation state due to the presence of vacant d orbitals.
Due to the small size of the fluorine atom, it is the most electronegative atom and due to this it is not able to show variable oxidation state.

Note:
Keep in mind that fluorine is the most electronegative and fluorine does not have vacant d orbital, thus it is only able to show $+ 1$ oxidation state and unable to show variable oxidation state like other halogens. All transition metals are d block elements but all d block elements are not transition metals.