How many types of unit cells are found in a primitive cubic unit cell?

$SrO$ has a $NaCl$ structure. If the lattice constant $a = 0.514 \ nm$ and the ionic radius of $Sr^{2+} = 0.113 \ nm$,what is the radius of the $O^{2-}$ ion?

Which of the following does not have a hexagonal crystal system?

Distinguish between
$(i)$ Hexagonal and monoclinic unit cells
$(ii)$ Face-centred and end-centred unit cells.

Identify the crystal system in which a primitive unit cell has edge lengths $a = b = 200 \text{ pm}$ and $c = 300 \text{ pm}$ and all axial angles are $90^{\circ}$.

Assertion : Graphite is an example of a tetragonal crystal system.
Reason : For a tetragonal system,$a = b \neq c$,$\alpha = \beta = 90^o$,$\gamma = 120^o$.