$a \ne b \ne c$,$\alpha \ne \beta \ne \gamma \ne 90^{\circ}$ represent:

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

The correct option for axial distances and axial angles for hexagonal crystal system is

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

Which among the following pairs of compounds is $NOT$ isomorphous?

$SrO$ 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?