Final answer:
To rank compounds in order of decreasing acidity, consider electronegativity and number of oxygen atoms. To rank compounds in order of increasing basicity, consider electronegativity of the central atom.
Step-by-step explanation:
To rank compounds in order of decreasing acidity, you need to consider the factors that affect acid strength. One important factor is the electronegativity of the central atom in oxyacids. The higher the electronegativity, the stronger the acid. Another factor is the number of oxygen atoms attached to the central atom; more oxygen atoms result in a stronger acid. For example, in the series H₃PO₄, CH₃PO₃, H₂, and HClO₃, HClO₃ is the strongest acid because Cl is the most electronegative and it has the highest number of oxygen atoms. Therefore, the correct order from most acidic to least acidic is HClO₃, H₃PO₄, CH₃PO₃, H₂.
To rank compounds in order of increasing basicity, you need to consider the factors that affect base strength. In general, the less electronegative the central atom in an anion, the stronger the base. For example, in the series CH₃S¯, OH¯, and CF₃S¯, CF₃S¯ is the strongest base because F is the most electronegative. Therefore, the correct order from least basic to most basic is CH₃S¯, OH¯, CF₃S¯.