Which of the following crystals has the unit cell such that $a=b \neq c$ and $\alpha=\beta=90^{\circ}$,$\gamma=120^{\circ}$?

The relation between axis and angles $a \neq b \neq c$ and $\alpha = \gamma = 90^{\circ}, \beta \neq 90^{\circ}$ corresponds to which crystal system?

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

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

Explain the concept of a two-dimensional lattice and a hypothetical two-dimensional crystal.

$Assertion (A)$: 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