Based on their molecular structure, choose the stronger acid from each pair of binary acids, and explain your choice: a. HF and HCl b. H2O and HF c. H2Se and H2S.

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1. Identify the periodic trend for acidity in binary acids: Acidity generally increases down a group in the periodic table due to the increase in atomic size, which weakens the H-X bond, making it easier to donate a proton.
2. For pair (a) HF and HCl: Compare the position of fluorine and chlorine in the periodic table. Chlorine is below fluorine, indicating that HCl is a stronger acid than HF due to the weaker H-Cl bond.
3. For pair (b) H2O and HF: Consider the electronegativity of the central atom. Fluorine is more electronegative than oxygen, which makes HF a stronger acid than H2O because the H-F bond is more polar, facilitating proton donation.
4. For pair (c) H2Se and H2S: Compare the position of selenium and sulfur in the periodic table. Selenium is below sulfur, suggesting that H2Se is a stronger acid than H2S due to the larger atomic size of selenium, which weakens the H-Se bond.
5. Summarize the findings: In each pair, the stronger acid is determined by either the position in the periodic table (for pairs a and c) or the electronegativity of the central atom (for pair b).