Which of the following properties indicate that an element is a metal. It I. reacts with oxygen to form an…

Analyze the question: We need to find which properties are characteristic of metals.

Check each statement:

• I. Reacts with oxygen to form an acidic oxide: False. Metals form basic oxides (or amphoteric ones). Non-metals form acidic oxides, such as CO₂ and SO₂.
• II. Forms ionic chlorides: True. Metals lose electrons to form cations, so their chlorides are ionic (NaCl, MgCl₂). Some metal chlorides like AlCl₃ are partly covalent, but this is the general metallic property.
• III. Has variable oxidation states: This is typical of transition metals (Fe²⁺/Fe³⁺, Cu⁺/Cu²⁺), but not of all metals. Na, K, Mg and Ca have only one oxidation state. Non-metals such as sulfur and nitrogen also show variable oxidation states, so it does not reliably indicate a metal.
• IV. Displaces hydrogen from dilute HCl: True for metals above hydrogen in the reactivity series (Mg, Zn, Fe). This is a classic test of metallic character, although unreactive metals like Cu and Ag do not do it.

Conclusion: The properties that indicate a metal are II and IV only.

Tip: Metals form basic oxides, ionic chlorides, and release H₂ from acids. Non-metals form acidic oxides and covalent chlorides. Don't be misled by "variable oxidation states", as it is not exclusive to metals.