If someone in chemistry could me with this with explanation

1.)read the following statements. which ones are correct? be sure to explain how you know.

bf3 and pf5 are examples of violations of the octet rule.
bf4− and bf3-nh3 are examples of violations of the octet rule.
expanded valence shells occur most often when the central atom is bonded to a small, electronegative element.
the central atoms most capable of having expanded valence shells come from rows 3, 4, and 5 of the periodic table.

2.)what is the steric number and the bond angles associated with each of the following molecules if a is the central atom, x refers to the atoms bonded to it and there are no lone pairs on the central atom.

ax3
ax4
ax6