Transition metal and their compounds are used as catalyst in industry and in biological system. For example, in the Contact Process, vanadium compounds in the +5 state `(V_(2)O_(5) or VO_(3)^(-))` are used to oxidise `SO_(2)` to `SO_(3)`:
`SO_(2)+(1)/(2)O_(2) overset(V_(2)O_(5))(to) SO_(3)`
It is thought thta the actual oxidation process takes place in two stages. In the first step, `V^(5+)` in the presence of oxide ions converts `SO_(2)` to `SO_(3)`. At the same time, `V^(5+)` is reduced to `V^(4+)`.
`2V^(5+)+O^(2-)+SO_(2) to 2V^(4+)+SO_(3)`
In the second step, `V^(5+)` is regenerated from `V^(4+)` by oxygen:
`2V^(4+)+(1)/(2)O_(2) to 2V^(5+)+O^(2-)`
The overall process is, of curse, the sum of these two steps:
`SO_(2) +(1)/(2)O_(2) to SO_(3)`
Q. Catalytic activity in transition metals depends on:

Options

A. Their ability to exist in different oxidation states
B. The size of the metal atoms
C. The number of empty atomic orbitals available
D. None of these

Answer

A