Which of the following is true regarding the transition elements?

a. multiple oxidation states resulting from the involvement of d electrons in bonding is a characteristic of transition elements.
b. changes in atomic radii in transition elements are greater than those in the main group elements.
c. most transition elements have lower melting and boiling points than the main group elements.
d. transition elements have predictable reactivity patterns.

Option (A) is the correct answer.

Explanation:

Transition elements are the elements that have incompletely filled d-orbitals. Their general electronic configuration is ns (n-1)d.

For example, Ti has atomic number 22 and its electronic configuration is .

Due to similar energies in ns and (n-1)d orbitals electrons can be easily transferred. This causes transition metals to show variable oxidation states.

Thus, we can conclude that it is true regarding the transition elements  that multiple oxidation states resulting from the involvement of d electrons in bonding is a characteristic of transition elements.