Which of the following statements is true?

The “spin-only” magnetic moment [in units of Bohr magneton, (µ_B)] of Ni²⁺ in aqueous solution would be : (Atomic number of Ni = 28)

Lanthanoid contraction is caused due to :

Nickel (Z = 28) combines with a uninegative monodentate ligand X^– to form a paramagnetic complex [NiX₄]²⁻ . The number of unpaired electron(s) in the nickel and geometry of this complex ion are, respectively