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Chemistry Chapter 4 : Topic 9
Electron Energy Levels
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An unknown element X has the following properties:
Reasoning: Metals are shiny, conduct electricity, and form positive ions. These properties strongly indicate an element from Group 1 or 2.
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An element Y reacts vigorously with water to produce hydrogen gas and a strong alkaline solution. Where is Y most likely located in the Periodic Table?
Reasoning: Only alkali metals react strongly with water to form hydroxides and hydrogen gas.
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An element has 7 electrons in its outermost shell and forms a diatomic molecule in its elemental state. It is most likely:
Reasoning: Elements with 7 valence electrons are halogens (Group 17), which exist as diatomic molecules like Cl₂.
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An unknown element Z is hard, has a high melting point, and forms acidic oxides. It is most likely:
Reasoning: Non-metals typically form acidic oxides and have relatively high melting points (like carbon or sulfur).
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Element A has atomic number 12. Without using the periodic table directly, its properties suggest it is:
Reasoning: Atomic number 12 corresponds to magnesium, a metal that forms basic oxides.
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An element shows the following behavior:
Reasoning: Non-metals generally gain electrons and are poor conductors.
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An element forms an oxide that dissolves in water to give a strong acid. This element is likely in:
Reasoning: Halogens form acidic oxides and acids like HCl, HBr.
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A substance is chemically inert, exists as monoatomic gas, and does not form compounds easily. It belongs to:
Reasoning: Noble gases are inert due to stable electronic configuration.
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An unknown element forms ionic compounds with chlorine and has two electrons in its outer shell. It is most likely:
Reasoning: Two valence electrons indicate Group 2 elements.
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Element X has properties:
Reasoning: Non-metals are brittle and form covalent bonds.
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An element reacts with oxygen to form a basic oxide and is highly reactive. It is most likely found in:
Reasoning: Metals on the left side form basic oxides.
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An element has atomic number 17. It is expected to:
Reasoning: Atomic number 17 (chlorine) gains 1 electron to achieve stability.
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A substance conducts electricity only when molten or dissolved in water. It is likely:
Reasoning: Ionic compounds conduct electricity in molten / aqueous state due to free ions.
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An element has high ionization energy and low reactivity. It is most likely:
Reasoning: Noble gases have very high ionization energy and are inert.
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An unknown element forms + 1 ions easily and is stored under oil due to high reactivity. It belongs to:
Reasoning: Alkali metals form + 1 ions and are highly reactive.
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An element forms acidic oxide and is located on the right side of Periodic Table. It is most likely:
Reasoning: Non-metals are located on the right and form acidic oxides.
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An element has 3 valence electrons and forms covalent as well as ionic compounds. It is likely:
Reasoning: Group 13 elements have 3 valence electrons and show variable bonding.
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An unknown element X is:
Reasoning: Sodium is a highly reactive alkali metal stored in kerosene.
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An element forms covalent molecules and exists as diatomic gas. It is most likely:
Reasoning: Chlorine exists as Cl₂, a diatomic covalent molecule.
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An element has a full outer shell and does not react easily. It is placed in:
Reasoning: Full outer shell corresponds to noble gases.
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