Argon crystallizes in such a way that the positions of the atoms are at $(0, 0, 0)$,$(0, 1/2, 1/2)$,$(1/2, 0, 1/2)$,and $(1/2, 1/2, 0)$. The type of unit cell is:

$A$ 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:

Calculate the total volume occupied by all atoms in a simple cubic unit cell if the radius of the atom is $3 \times 10^{-8} \ cm$.

The sum of the number of first and second nearest neighbors in an $FCC$ closed packing is:

For a tetrahedral structure,the limiting radius ratio $r_c^+ / r_a^-$ is .......

In a face centered cubic lattice,atoms $A$ are at the corner points and atoms $B$ are at the face centered points. If one atom $B$ is missing from one of the face centered points,the formula of the ionic compound is: