Consider $3$ crystals (all having FCC lattice) labelled as $\text{P, Q}$ and $\text{R}$ as described below:
- Crystal $\text{P}$: Cu crystal with $4$ $\text{Cu}$ atoms per unit cell
- Crystal $\text{Q}$: NaCl crystal with $4 \mathrm{Na}^{+}$ions and $4 \mathrm{Cl}^{-}$ions per unit cell
- Crystal $\text{R}$: Diamond crystal with $8$ $\text{C}$ atoms per unit cell
Which of the following options is/are correct?
- Only crystal $\text{P}$ is a close packed structure.
- Only crystal $\text{Q}$ is a close packed structure.
- Crystal $\text{R}$ has the smallest packing factor.
- All the crystals $\text{P, Q}$ and $\text{R}$ are close packed structures.
