This question tests understanding of valence electrons and ionic compounds. Potassium (Z=19) is in Group 1 with electron configuration [Ar]4s¹, meaning it has 1 valence electron in the fourth shell. To achieve the stable argon configuration (18 electrons), potassium loses its single valence electron to form K⁺. The K²⁺ option (A) is incorrect because losing 2 electrons would remove an electron from the filled 3p orbital, requiring much more energy and creating an unstable configuration that doesn't match any noble gas. Group 1 elements always form +1 cations by losing their single valence electron.

This question assesses the skill of valence electrons and ionic compounds. Valence electrons influence ion formation by showing how many electrons are gained or lost for stability. Element P with atomic number 9 is fluorine in Group 17, with 7 valence electrons, and it gains 1 electron to form a -1 ion. This achieves the stable configuration of neon. A tempting distractor is +1, but it is incorrect because halogens are nonmetals that gain electrons, not lose them. Main-group ions form to achieve noble-gas configurations by gaining or losing the fewest electrons possible.

This question assesses the skill of valence electrons and ionic compounds. Valence electrons determine an atom's stability and likelihood of forming ions. Noble gases in Group 18, like element N, have 8 valence electrons, completing their octet and making them stable without needing to gain or lose electrons. Thus, they do not commonly form monatomic ions under typical conditions. A tempting distractor is that N forms $N^{2-}$ to complete an octet, but it is incorrect because noble gases already have a complete octet. Main-group ions form to achieve noble-gas configurations, but noble gases are already stable and rarely ionize.

This question assesses the skill of valence electrons and ionic compounds. Valence electrons determine ion formation by indicating whether an atom will gain or lose electrons for stability. Group 16 elements have 6 valence electrons and typically gain 2 electrons to complete an octet, forming anions with a -2 charge. This results in a noble-gas-like configuration, making $Q^{2-}$ the most stable monatomic ion for element Q. A tempting distractor is $Q^{2+}$, but it is incorrect because nonmetals in Group 16 gain electrons rather than lose them to form negative ions. Main-group ions form to achieve noble-gas configurations by gaining or losing the fewest electrons possible.

This question assesses the skill of valence electrons and ionic compounds. Valence electrons are the outermost electrons in an atom that participate in chemical bonding and determine the ion's charge. For elements in Group 17, like element X with atomic number 17, there are 7 valence electrons, and these elements tend to gain 1 electron to achieve a stable octet configuration similar to noble gases. This gain of one electron results in a monatomic ion with a charge of -1. A tempting distractor is +7, but it is incorrect because losing 7 electrons would require too much energy for a nonmetal, and nonmetals typically gain electrons rather than lose them. Main-group ions form to achieve noble-gas configurations by gaining or losing the fewest electrons possible.

This question assesses the skill of valence electrons and ionic compounds. Valence electrons determine the charges of ions, which in turn dictate the formulas of ionic compounds. Element T in Group 1 has 1 valence electron and forms a +1 ion, while W in Group 16 has 6 valence electrons and forms a -2 ion. To balance charges, two T ions combine with one W ion, resulting in the formula T_2W. A tempting distractor is TW, but it is incorrect because it does not account for the -2 charge of W requiring two +1 ions for neutrality. Main-group ions form to achieve noble-gas configurations, and compound formulas balance total positive and negative charges.

This question assesses the skill of valence electrons and ionic compounds. Valence electrons help predict ion charges based on an element's position in the periodic table. Group 13 elements like S have 3 valence electrons and lose them to form +3 ions, attaining a noble-gas configuration. This is typical for metals in this group, such as aluminum. A tempting distractor is $S^{3-}$, but it is incorrect because Group 13 elements are metals that lose electrons, not gain them like nonmetals. Main-group ions form to achieve noble-gas configurations by losing or gaining the fewest electrons possible.

This question assesses the skill of valence electrons and ionic compounds. Valence electrons are located in the highest energy level and influence an atom's reactivity and ion formation. For element Z with atomic number 13, which is in Group 13, the electron configuration ends with 3 valence electrons in the s and p orbitals. These 3 valence electrons can be lost to form a +3 ion, aligning with the group's tendency to achieve noble-gas stability. A tempting distractor is 13, but it is incorrect as it represents the total electrons, not just the valence ones. Main-group ions form to achieve noble-gas configurations by losing or gaining the fewest electrons possible.

This question assesses the skill of valence electrons and ionic compounds. Valence electrons play a key role in predicting ion charges as atoms lose or gain them to attain stable configurations. Element M with atomic number 12 is in Group 2 and has 2 valence electrons, which it loses to form a +2 ion, matching the noble gas neon's configuration. This +2 charge is common for alkaline earth metals due to their metallic nature. A tempting distractor is $M^{2-}$, but it is incorrect because metals lose electrons to form positive ions, not gain them. Main-group ions form to achieve noble-gas configurations by losing or gaining the fewest electrons possible.

This question tests understanding of valence electrons and ionic compounds. Chlorine (Z=17) has an electron configuration of 1s²2s²2p⁶3s²3p⁵, giving it 7 valence electrons in the third shell. To achieve a noble-gas configuration like argon (18 electrons), chlorine needs to gain 1 electron, forming Cl⁻. The Cl²⁻ option (A) is incorrect because gaining 2 electrons would give chlorine 19 electrons total, exceeding argon's configuration and creating an unstable ion with excess negative charge. When forming ionic compounds, main-group elements gain or lose the fewest electrons possible to achieve the nearest noble-gas configuration.