Variable valency,in general,is exhibited by

The maximum number of unpaired electrons is present in

Which among the following elements does $NOT$ exhibit ferromagnetic properties?

Observe the following ions: $V^{2+}, Zn^{2+}, Cu^{2+}, Fe^{2+}, Fe^{3+}, Ti^{3+}, Sc^{3+}, Ti^{4+}, Ni^{3+}, Co^{3+}, Cu^+$. How many ions in the above list have zero magnetic moment?

Which group of elements is known as coinage metals?

Which of the following ions has the maximum theoretical magnetic moment?