\begin{tabular}{l} Which of the following will pair \\ with a group 7 halogen, such as \\ bromine (Br), in a 1:1 ratio, \\ based on trends in valence \\ electrons? \\ \hline barium(Ba) \\ \hline aluminum (A) \\ \hline sulfur(S) \\ \hline potassium (K) \\ \hline\end{tabular}

To determine which of the given elements will pair with a Group 17 halogen (such as bromine, Br) in a 1:1 ratio, we need to consider the typical oxidation states of each element and how they balance with the halogen's oxidation state. ### **Understanding Oxidation States:** - **Halogens (Group 17):** Typically have an oxidation state of **-1** when forming ionic compounds. - **Given Elements:** - **Barium (Ba):** Group 2 element with an oxidation state of **+2**. - **Aluminum (Al):** Group 13 element with an oxidation state of **+3**. - **Sulfur (S):** Group 16 element, typically has an oxidation state of **-2** (acting as an anion in compounds, not likely to pair with halogens in a 1:1 ratio). - **Potassium (K):** Group 1 element with an oxidation state of **+1**. ### **Pairing with Bromine:** - **Barium (Ba):** - **Oxidation State:** +2 - **Pairing Ratio:** Would require two bromine atoms to balance the charge (BaBr₂) - **Aluminum (Al):** - **Oxidation State:** +3 - **Pairing Ratio:** Would require three bromine atoms to balance the charge (AlBr₃) - **Sulfur (S):** - **Oxidation State:** -2 - **Pairing with Bromine:** Not typically forming 1:1 ionic compounds with halogens. - **Potassium (K):** - **Oxidation State:** +1 - **Pairing Ratio:** Requires one bromine atom to balance the charge (KBr) ### **Conclusion:** **Potassium (K)** is the element that will pair with a Group 17 halogen like bromine (Br) in a **1:1 ratio**, forming compounds such as potassium bromide (KBr). **Answer:** Potassium (K) will form a 1:1 compound with bromine.