Aqueous solution of which salt will not contain ions with the electronic configuration $1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6$?

Which of the following sets of quantum numbers is correct for an electron in a $3d$-orbital?

Total number of ions from the following with noble gas configuration is . . . . . . .
$Sr^{2+} (Z=38), Cs^{+} (Z=55), La^{2+} (Z=57), Pb^{2+} (Z=82), Yb^{2+} (Z=70) \text{ and } Fe^{2+} (Z=26)$

What is the difference between $2p_x, 2p_y,$ and $2p_z$ orbitals?

The valence shell electronic configuration is $(n - 1)s^2 (n - 1)p^6 (n - 1)d^x ns^2$. If $n = 4$ and $x = 5$,what is the number of protons in the element?

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.