What are the likely ground-state electron configurations of the following anions? (a) Se^2- (b) N^3-

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1. Identify the atomic number of the neutral atom. Selenium (Se) has an atomic number of 34, and nitrogen (N) has an atomic number of 7.
2. Determine the electron configuration of the neutral atom. For Se, the electron configuration is [Ar] 3d^{10} 4s^{2} 4p^{4}. For N, it is 1s^{2} 2s^{2} 2p^{3}.
3. Add electrons to account for the charge of the anion. For Se^{2-}, add 2 electrons to the neutral Se configuration, resulting in [Ar] 3d^{10} 4s^{2} 4p^{6}. For N^{3-}, add 3 electrons to the neutral N configuration, resulting in 1s^{2} 2s^{2} 2p^{6}.
4. Recognize that adding electrons to the p orbitals fills them to their maximum capacity, achieving a noble gas configuration. Se^{2-} achieves the configuration of Kr, and N^{3-} achieves the configuration of Ne.
5. Verify that the resulting electron configurations correspond to stable, filled-shell configurations, which are characteristic of noble gases.