The nitrate ion, NO3–, does not violate the octet rule because it has a stable electron configuration. In NO3–, nitrogen is the central atom surrounded by three oxygen atoms. The nitrogen atom has five valence electrons, and each oxygen atom contributes two electrons through single or double bonds. This allows the nitrogen to effectively share its electrons, achieving a full octet through resonance structures where the negative charge is delocalized over the three oxygen atoms.
On the other hand, BCl3 (boron trichloride) does indeed violate the octet rule. Boron has only three valence electrons and forms three single bonds with chlorine atoms. In doing so, boron ends up with only six electrons in its outer shell, which is less than the eight required for a full octet. This is permissible because boron is an exception to the octet rule; it is a small atom that can be stable with fewer than eight electrons, often leading to a strong affinity for electron-pair donors (Lewis bases).