Which rule is violated in the given electronic configuration?

In $Cu$ (Atomic number $Z = 29$),which of the following statements regarding the electron spin is correct?

Which of the following is the correct electronic configuration of $Cr$ (Chromium)?

Choose the pair whose ions have the similar electronic configuration.

The maximum number of sub-levels, orbitals and electrons in $N$ shell of an atom are respectively

The extra stability of half-filled subshells is due to:
$(A)$ Symmetrical distribution of electrons
$(B)$ Smaller coulombic repulsion energy
$(C)$ The presence of electrons with the same spin in non-degenerate orbitals
$(D)$ Larger exchange energy
$(E)$ Relatively smaller shielding of electrons by one another
Identify the correct statements.