Which of the following is ferromagnetic?

The electronic configuration of Gadolinium ($Gd$,$Z = 64$) is:

Determine whether the following statements are True $(T)$ or False $(F)$:
$(a)$ Transition elements contain $d$-orbitals.
$(b)$ Ions of transition elements contain incompletely filled $d$-orbitals.
$(c)$ Only elements with completely filled $3d$ orbitals are considered transition elements.
$(d)$ Only elements that have incompletely filled $d$-orbitals in their ground state as well as in their ions are called transition elements.

How is the variability in oxidation states of transition metals different from that of the non-transition metals? Illustrate with examples.

Name the periodic element,which does not show variable oxidation states.

Which one of the following ions exhibits the highest magnetic moment?