Q1. Which of the following represents the correct definition of a molecule?
a) A single atom bonded to another atom
b) A group of atoms held together by ionic bonds
c) Two or more atoms chemically bonded together
d) A substance composed of multiple elements
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Correct Answer: c) Two or more atoms chemically bonded together
Explanation: A molecule is defined as a stable, electrically neutral group of at least two atoms held together by covalent chemical bonds. These atoms may be of the same element or different elements. Covalent bonds involve the sharing of electron pairs between atoms, resulting in the formation of molecules. Molecules can be simple, such as diatomic molecules like oxygen (O2), or complex, such as organic compounds like glucose (C6H12O6). Understanding molecules is essential in chemistry, as they are the building blocks of matter and play key roles in various chemical reactions and biological processes.
Q2. What type of bond holds the atoms together in a molecule?
a) Ionic bond
b) Hydrogen bond
c) Covalent bond
d) Metallic bond
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Correct Answer: c) Covalent bond
Explanation: Covalent bonds are formed when atoms share one or more pairs of electrons to achieve a stable electron configuration. These bonds occur between nonmetal atoms and are responsible for holding atoms together in a molecule. Covalent bonds can be single, double, or triple, depending on the number of electron pairs shared between atoms. They are relatively strong compared to other types of bonds and play a crucial role in the formation and stability of molecules in various chemical compounds.
Q3. Which of the following is an example of a diatomic molecule?
a) Carbon dioxide (CO2)
b) Water (H2O)
c) Oxygen (O2)
d) Methane (CH4)
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Correct Answer: c) Oxygen (O2)
Explanation: Diatomic molecules consist of two atoms of the same element bonded together. Oxygen (O2) is a classic example of a diatomic molecule, where two oxygen atoms are covalently bonded to form a stable molecule. Other examples of diatomic molecules include nitrogen (N2), hydrogen (H2), fluorine (F2), chlorine (Cl2), and bromine (Br2). These molecules are frequently encountered in nature and have significant implications in various chemical reactions and processes.
Q4. Which term refers to a molecule with an uneven distribution of charge, resulting in a positive and a negative end?
a) Nonpolar molecule
b) Ionic molecule
c) Polar molecule
d) Covalent molecule
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Correct Answer: c) Polar molecule
Explanation: A polar molecule is characterized by an uneven distribution of electron density, leading to a separation of electric charge, with one end having a partial positive charge and the other end having a partial negative charge. This polarity arises when atoms within the molecule have different electronegativities, causing the shared electrons to be pulled more toward one atom than the other. Water (H2O) is a classic example of a polar molecule due to the electronegativity difference between hydrogen and oxygen atoms, resulting in a bent molecular geometry and a dipole moment.
Q5. Which of the following statements about molecules is true?
a) Molecules always consist of atoms of the same element.
b) Molecules can exist as single atoms.
c) Molecules are always electrically charged.
d) Molecules can be composed of atoms of different elements.
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Correct Answer: d) Molecules can be composed of atoms of different elements.
Explanation: Molecules can be composed of atoms of the same element, such as diatomic molecules, or atoms of different elements, forming chemical compounds. Compounds like water (H2O), carbon dioxide (CO2), and glucose (C6H12O6) are examples of molecules composed of different elements bonded together through covalent bonds. Understanding the composition and structure of molecules is essential in chemistry, as it provides insights into the properties and behavior of substances in various chemical reactions and environments.
Q6. Which of the following represents the correct definition of a molecule?
a) The smallest unit of an element that retains its chemical properties
b) A substance composed of only one type of atom
c) A combination of atoms held together by ionic bonds
d) A group of atoms that can exist independently
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Correct Answer: c) A combination of atoms held together by ionic bonds
Explanation: A molecule is defined as a stable, electrically neutral group of at least two atoms held together by covalent chemical bonds. Unlike ionic compounds, where atoms are held together by electrostatic attractions between positively and negatively charged ions, molecules involve the sharing of electron pairs between atoms to achieve stability. Molecules can vary in size and complexity, ranging from simple diatomic molecules like hydrogen (H2) to large, complex organic compounds like proteins and DNA.
Q7. Which of the following is an example of a molecule?
a) Sodium chloride (NaCl)
b) Oxygen gas (O2)
c) Iron (Fe)
d) Neon (Ne)
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Correct Answer: b) Oxygen gas (O2)
Explanation: Oxygen gas (O2) is an example of a molecule, specifically a diatomic molecule composed of two oxygen atoms covalently bonded together. Molecules are formed when atoms share electrons to achieve a stable electron configuration. Unlike ionic compounds, which consist of positively and negatively charged ions held together by electrostatic forces, molecules are electrically neutral and involve the sharing of electron pairs between atoms. Understanding molecules is essential in chemistry, as they are the building blocks of matter and play key roles in various chemical reactions and biological processes.
Q8. What is the term for a molecule consisting of three atoms?
a) Monatomic molecule
b) Diatomic molecule
c) Triatomic molecule
d) Polyatomic molecule
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Correct Answer: c) Triatomic molecule
Explanation: A triatomic molecule is a molecule composed of three atoms chemically bonded together. Examples of triatomic molecules include ozone (O3), carbon dioxide (CO2), and nitrogen dioxide (NO2). These molecules exhibit unique chemical and physical properties based on their molecular structures and compositions. Triatomic molecules are commonly encountered in atmospheric chemistry, where they play crucial roles in environmental processes and reactions.
Q9. Which of the following is an example of a nonpolar molecule?
a) Water (H2O)
b) Ammonia (NH3)
c) Methane (CH4)
d) Hydrochloric acid (HCl)
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Correct Answer: c) Methane (CH4)
Explanation: Methane (CH4) is an example of a nonpolar molecule. Nonpolar molecules have an even distribution of charge and lack distinct positive and negative ends. In methane, the carbon atom shares its electrons equally with the four hydrogen atoms, resulting in a symmetric molecular geometry and a net dipole moment of zero. Nonpolar molecules are typically composed of atoms with similar electronegativities or have symmetrical molecular structures that cancel out any net dipole moment.
Q10. What is the term for a group of atoms held together by covalent bonds that carry an electric charge?
a) Ionic compound
b) Polar molecule
c) Polyatomic ion
d) Metallic compound
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Correct Answer: c) Polyatomic ion
Explanation: A polyatomic ion is a group of atoms held together by covalent bonds that carry a net electric charge, making it an ion. Unlike simple ions, which consist of single atoms with a charge, polyatomic ions are composed of multiple atoms bonded together, and they exhibit distinct chemical properties. Polyatomic ions can be positively charged (cations) or negatively charged (anions) and are commonly encountered in ionic compounds and chemical reactions. Examples of polyatomic ions include sulfate (SO4^2-), nitrate (NO3^-), ammonium (NH4^+), and carbonate (CO3^2-). Understanding polyatomic ions is essential in chemistry, particularly in the study of acids, bases, and salts, where they play significant roles in chemical reactions and solution chemistry.