Coordination numbers of $Zn^{2+}$ and $S^{2-}$ in the crystal structure of wurtzite are

The radius of the largest sphere which fits properly at the centre of the edge of a body-centered cubic $(BCC)$ unit cell is (Edge length is represented by $a$) (in $a$)

$A$ crystal is made up of metal ions $M_1$ and $M_2$ and oxide ions. Oxide ions form a $ccp$ lattice structure. The cation $M_1$ occupies $50 \%$ of octahedral voids and the cation $M_2$ occupies $12.5 \%$ of tetrahedral voids of the oxide lattice. The oxidation numbers of $M_1$ and $M_2$ are,respectively:

Potassium crystallizes in a $bcc$ lattice,hence the coordination number of potassium in potassium metal is

How many unit cells are present in $39 \ g$ of potassium that crystallizes in a body-centered cubic $(BCC)$ structure? [Atomic weight of $K = 39$]

The number of $Cl^{-}$ ions around one $Na^{+}$ in $NaCl$ crystal lattice is