Which of the following groups of transition metals is known as coinage metals?

Which of the following statements is correct regarding the ions $Zn^{2+}$,$Ni^{2+}$,and $Cr^{3+}$? (Atomic numbers: $Zn = 30$,$Ni = 28$,$Cr = 24$)

What is the number of unpaired electrons in $f$ orbitals of lutetium in its $+3$ oxidation state?

Which of the following $3d$-metal ion will give the lowest enthalpy of hydration $(\Delta_{hyd}H)$ when dissolved in water?

Elements $A$ and $B$ do not form an alloy because....

Identify the element if its observed and expected electronic configuration is considered,specifically focusing on the transition metal series where $d$-orbital filling occurs.