The three-dimensional graph of lattice points which sets the pattern for the whole lattice is called:

How many lattice points are present in a face-centred cubic unit cell?

$Assertion (A)$: White tin is an example of a tetragonal system. $Reasoning (R)$: For a tetragonal system, $a=b=c$ and $\alpha=\beta=\gamma \neq 90^{\circ}$. The correct answer is

Lithium forms $BCC$ structure having an edge length of unit cell $351 \ pm$. What is the atomic radius of lithium (in $pm$)?

Enlist the characteristics of a unit cell.

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