I think O and Cl will form covalent bonds since they are both non-metals and don't have a large enough difference in electronegativities to create an ionic bond.
I hope this helps. Let me know if anything is unclear.
Answer:

Explanation:
As can be seen in the Figure in a face-centered cubic unit cell you have:
- Six halves of atoms
- Eight 1/8 of atom (1 in each corner)
In total:

Now, each side of the cell is 234 picometers (2.34e-8 cm) long


Atoms per cm3:


Expressing in mass:

