Which of the following is a unique quantity of an element?
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Every element has a unique number of protons.
A pure substance that contains only one type of atom is called
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Think about what defines an element.
Which of the following is not a pure substance?
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Pure substances are elements or compounds only.
A pure substance can only be
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Pure substances include both elements and compounds.
The smallest particle of an element that takes part in chemical reactions is
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Electrons alone do not take part in chemical reactions as independent units.
Which of the following sequences is correct if the given elements are arranged according to ascending atomic number?
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Fe=26, Co=27, Ni=28, Cu=29.
Which one of the following is not a mixture?
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Distilled water is a pure substance (compound).
Which of the following elements does not show variable valency?
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Zinc always has a valency of 2 (Zn2+) in all its compounds.
The atomic number of calcium is
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Atomic number = number of protons. Atomic mass of Ca is 40.
The symbolic representation of a molecule of an element or a compound is called
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The molecular formula shows the actual number of atoms in a molecule.
The atomicity of helium is
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Noble gases exist as monoatomic molecules.
The valency of an element depends upon
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Valency is determined by the number of electrons an atom can gain/lose/share.
Which of the following is a compound?
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A compound contains two or more different elements chemically combined. Water = H2O.
Which statement is erroneous?
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Calcium always has valency 2; it does not show variable valency.
Which of the following is not a molecule?
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A single hydrogen atom (H) does not have independent existence; it exists as H2.
The formula that represents the exact number of atoms in a molecule is
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The empirical formula shows only the simplest ratio — not the exact count.
Variable valency is generally shown by
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Transition (d-block) elements have incompletely filled d-orbitals allowing variable oxidation states.
