This question tests understanding of atomic structure and electron configuration. An element with atomic number 26 has 26 electrons in its neutral state. Electrons fill orbitals following the Aufbau principle in the order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, etc. For 26 electrons: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18), 4s² (20), 3d⁶ (26 total). Option E incorrectly shows 3d⁵ instead of 3d⁶, which would only account for 25 electrons. When writing electron configurations, always count electrons systematically and remember that 4s fills before 3d.

This question tests the skill of atomic structure and electron configuration. Atomic number 24 means chromium with 24 electrons, but it is an exception to the Aufbau principle for stability. Normally, electrons would fill 4s² 3d⁴, but chromium prefers half-filled d subshell, so it is 4s¹ 3d⁵. This configuration provides extra stability due to the half-filled subshells. A tempting distractor like A, [Ar] 4s² 3d⁴, is incorrect because it ignores the exception for chromium and copper in the periodic table. Remember exceptions for elements like Cr and Cu where half-filled or fully filled d subshells are preferred for stability.

This question tests the skill of atomic structure and electron configuration. The configuration [He] 2s² 2p⁴ is oxygen with 8 electrons. In 2p⁴, Hund's rule places electrons in three orbitals: two paired in one, and two unpaired in others. This results in two unpaired electrons total. The pairing minimizes energy while following rules. A tempting distractor like A, 0, is incorrect as it assumes all paired, ignoring Hund's distribution. Use orbital diagrams to visualize electron pairing and count unpaired electrons in p subshells.

This question tests the skill of atomic structure and electron configuration. Atomic number 13 is aluminum with 13 electrons neutrally, but Q³⁺ loses 3, leaving 10. Ions form by removing electrons from outermost orbitals, here 3s and 3p. The resulting configuration is 1s² 2s² 2p⁶, matching neon's. A tempting distractor like E, 1s² 2s² 2p⁶ 3s¹, is incorrect as it retains an electron in 3s, not fully ionizing to 3+. For cations, remove electrons from valence shells first and verify total matches atomic number minus charge.

This question tests your understanding of atomic structure and electron configuration. A neutral atom with atomic number 12 has 12 electrons. Electrons fill orbitals in order: 1s² (2), 2s² (4), 2p⁶ (10), and 3s² (12 total). This configuration for magnesium follows the Aufbau principle without exceptions. A tempting distractor is choice E (1s² 2s² 2p⁶ 4s²), which skips the 3s orbital, but 3s fills before 4s. Count the total electrons and fill subshells in sequence: 1s, 2s, 2p, 3s, 3p, 4s, etc.

This question tests your understanding of atomic structure and electron configuration. A neutral atom with atomic number 20 has 20 electrons. Electrons fill up to $[\mathrm{Ar}]$ (18 electrons), then $4s^2$ for the remaining 2, resulting in $[\mathrm{Ar}],4s^2$ for calcium. This follows the standard order without exceptions. A tempting distractor is choice C ($[\mathrm{Ne}],3s^2,3p^6,4s^2$), which expands Ar correctly but is less concise than using [Ar]. Start with the nearest noble gas core and add valence electrons for simplified configurations.

This question involves atomic structure and electron configuration, specifically counting unpaired electrons. The configuration [Kr]5s²4d⁵ shows a filled 5s subshell and a half-filled 4d subshell. The d subshell has 5 orbitals, and with 5 electrons following Hund's rule, each electron occupies a separate orbital with parallel spins. This results in 5 unpaired electrons in the 4d subshell (the 5s electrons are paired). The tempting distractor B (3 unpaired) might come from incorrectly pairing some 4d electrons, but Hund's rule requires maximum unpaired electrons before pairing begins. To count unpaired electrons, examine each partially filled subshell and apply Hund's rule to determine electron distribution.

This question involves atomic structure and electron configuration for anions. Element Z has atomic number 15 (phosphorus), so a neutral atom has 15 electrons. The Z³⁻ ion has gained 3 electrons, giving it 18 electrons total. Following the Aufbau principle: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18 total). This configuration is identical to argon, a noble gas, which makes sense as ions often achieve noble gas configurations for stability. The tempting distractor A shows only 17 electrons (3p⁵), which would be the configuration for a neutral chlorine atom, not P³⁻. When dealing with anions, add the charge magnitude to the atomic number to find the total electron count, then fill orbitals accordingly.

This question requires understanding atomic structure and electron configuration to identify the highest-energy occupied orbital. The configuration [Ne]3s²3p⁴ shows electrons filling through the 3p subshell. In multi-electron atoms, energy increases with both principal quantum number (n) and orbital type, following the order: 1s < 2s < 2p < 3s < 3p < 4s < 3d, etc. Since 3p is the last (highest) occupied subshell in this configuration, it contains the highest-energy electrons. The tempting distractor B (3s) is incorrect because 3s electrons are lower in energy than 3p electrons within the same principal energy level. To find the highest-energy electrons, identify the last subshell written in the electron configuration.

This question involves atomic structure and electron configuration of ions. The neutral atom has configuration [Ar]4s²3d¹⁰4p⁵, which means it has 35 electrons (18 from Ar + 2 + 10 + 5). When this atom gains one electron to form a 1- ion, the electron enters the lowest available orbital, which is the 4p subshell. The 4p subshell can hold 6 electrons total, so 4p⁵ becomes 4p⁶, giving [Ar]4s²3d¹⁰4p⁶. Option B incorrectly places the extra electron in the 4d orbital, which is higher in energy than completing the 4p subshell. Remember that electrons always fill the lowest energy orbital available first.