$A$ unit cell having dimensions $a \neq b \neq c$ and interfacial angles $\alpha \neq \beta \neq \gamma \neq 90^{\circ}$ is known as:

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 $90^{\circ}$.

$Assertion (A)$: 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

Crystals can be classified into how many basic crystal systems?

Explain the Bravais lattices with examples and characteristics.

Chromium metal crystallises in a body-centred cubic $(bcc)$ lattice. The edge length of the unit cell is found to be $287 \, pm$. The atomic radius of chromium will be ............. $pm$.