Final answer:
The central atom that violates the octet rule is (d) NO₃⁻, which is the nitrate ion.
Step-by-step explanation:
The central atom that violates the octet rule is (d) NO₃⁻, which is the nitrate ion. The octet rule states that atoms tend to gain, lose, or share electrons to achieve a full outer electron shell with 8 electrons. However, in the nitrate ion, the central nitrogen atom has 5 covalent bonds and a total of 24 electrons around it.