1. A chemical bond is best described as
ⓐ. an attraction that exists only after atoms become isolated ions
ⓑ. a contact between atoms without any electron interaction
ⓒ. a temporary grouping of atoms with no stability change
ⓓ. attraction holding atoms or ions together
Correct Answer: attraction holding atoms or ions together
Explanation: A chemical bond is an attractive force that keeps atoms or ions together in a stable arrangement. It may arise through electron transfer, electron sharing, or other bonding interactions. The word "bond" does not mean that atoms simply touch each other mechanically. Bonding is connected with stability and energy lowering in a chemical species. In \(\mathrm{NaCl}\), ions are held together by attraction, while in \(\mathrm{H_2}\), atoms are held together by shared electrons.
2. Atoms usually combine with other atoms because the combined arrangement is generally
ⓐ. higher in energy and less stable
ⓑ. lower in energy and more stable
ⓒ. unchanged in energy and always reactive
ⓓ. independent of electron arrangement
Correct Answer: lower in energy and more stable
Explanation: Atoms combine when the resulting bonded system is more stable than the separated atoms. Greater stability usually corresponds to lower energy. This idea is broader than simply saying that every atom wants an octet, because some stable species do not follow the octet rule exactly. Bond formation is therefore best understood as a movement toward a favourable energy state. Rules such as duplet and octet are useful guides, but the deeper reason is stability.
3. The attraction in solid \(\mathrm{NaCl}\) is mainly between
ⓐ. neutral \(\mathrm{Na}\) atoms and neutral \(\mathrm{Cl}\) atoms
ⓑ. two identical negative ions
ⓒ. positive \(\mathrm{Na^+}\) ions and negative \(\mathrm{Cl^-}\) ions
ⓓ. separate \(\mathrm{NaCl}\) molecules joined by weak forces only
Correct Answer: positive \(\mathrm{Na^+}\) ions and negative \(\mathrm{Cl^-}\) ions
Explanation: In \(\mathrm{NaCl}\), sodium loses an electron to form \(\mathrm{Na^+}\), while chlorine gains an electron to form \(\mathrm{Cl^-}\). The solid is held together by electrostatic attraction between oppositely charged ions. It is not best described as a collection of separate neutral \(\mathrm{NaCl}\) molecules. This example shows ionic bonding in a simple way while keeping the focus on charge formation and electrostatic attraction. The sign of charge matters because like charges repel and unlike charges attract.
4. The electrons most directly involved in ordinary chemical bonding are
ⓐ. the outermost shell electrons
ⓑ. only the filled inner-shell electrons
ⓒ. only the innermost shell electrons
ⓓ. the total mass of the atom
Correct Answer: the outermost shell electrons
Explanation: The electrons in the outermost shell are called valence electrons. These electrons are most available for loss, gain, or sharing during chemical bonding. Inner shell electrons are held more tightly and usually do not directly participate in ordinary bonding for main-group elements. Valence electrons also help explain valency, ion formation, and Lewis symbols. This is why the outer shell is central when drawing Lewis structures.
5. A noble-gas configuration is often used as a stability reference because noble gases generally have
ⓐ. outer shells that are still partly filled
ⓑ. completed outer electron shells
ⓒ. no electrons in their outermost shell
ⓓ. only metallic bonding in every state
Correct Answer: completed outer electron shells
Explanation: Noble gases are usually chemically less reactive because their outer electron shells are already stable. Many atoms form bonds in ways that move them toward a similar stable electron arrangement. For hydrogen and helium, a duplet arrangement is relevant, while many main-group atoms are discussed using the octet rule. This does not mean that every stable molecule must obey an octet exactly. The noble-gas idea is a useful starting point, not a universal explanation for every bonded species.
6. The description that best separates \(\mathrm{O_2}\) from \(\mathrm{CO_2}\) is
ⓐ. \(\mathrm{O_2}\) is a compound, while \(\mathrm{CO_2}\) is an element
ⓑ. \(\mathrm{O_2}\) contains two different elements, while \(\mathrm{CO_2}\) contains one element
ⓒ. \(\mathrm{O_2}\) is a molecule of an element, while \(\mathrm{CO_2}\) is a molecular compound
ⓓ. both \(\mathrm{O_2}\) and \(\mathrm{CO_2}\) are ionic compounds
Correct Answer: \(\mathrm{O_2}\) is a molecule of an element, while \(\mathrm{CO_2}\) is a molecular compound
Explanation: \(\mathrm{O_2}\) contains only oxygen atoms, so it is a molecule of an element. \(\mathrm{CO_2}\) contains carbon and oxygen atoms chemically bonded in a fixed composition, so it is a compound. Both are molecular in nature, but they are not classified in the same way. A molecule can be made from atoms of the same element or from atoms of different elements. The word compound is used only when two or more different elements are chemically combined.
7. Assertion: Bond formation is often associated with a decrease in energy of the system.
Reason: A lower-energy arrangement is generally more stable than a higher-energy arrangement.
ⓐ. Both Assertion and Reason are true, but Reason does not explain Assertion
ⓑ. Assertion is true, but Reason is false
ⓒ. Assertion is false, but Reason is true
ⓓ. Both Assertion and Reason are true, and Reason explains Assertion
Correct Answer: Both Assertion and Reason are true, and Reason explains Assertion
Explanation: A bonded arrangement is usually favoured when it has lower energy than the separated particles. Stability and lower energy are closely related in chemical bonding. The Reason explains why atoms do not combine randomly into every possible arrangement. Only arrangements that are sufficiently favourable can persist as stable substances. Octet completion is one common way to reach stability, but energy lowering is the broader idea behind bonding.
8. In bonding terminology, the valence shell means
ⓐ. the innermost occupied electron shell of an atom
ⓑ. the space between two bonded atoms only
ⓒ. the shell that must always contain \(8\) electrons
ⓓ. the outermost occupied electron shell of an atom
Correct Answer: the outermost occupied electron shell of an atom
Explanation: The valence shell is the outermost shell that contains electrons in an atom. Electrons in this shell are called valence electrons. These electrons control many bonding tendencies of main-group elements. The valence shell does not always contain exactly \(8\) electrons; atoms may have fewer before bonding or may follow other stable arrangements. This term is important because Lewis symbols and bonding rules are built from valence-shell electrons.
9. A sample of pure water contains \(\mathrm{H_2O}\) molecules. This means that each molecule contains
ⓐ. separated hydrogen and oxygen atoms with no fixed ratio
ⓑ. bonded hydrogen and oxygen in a fixed ratio
ⓒ. only oxygen atoms arranged in pairs
ⓓ. sodium and chloride ions arranged alternately
Correct Answer: bonded hydrogen and oxygen in a fixed ratio
Explanation: The formula \(\mathrm{H_2O}\) shows that each water molecule contains hydrogen and oxygen atoms in a fixed ratio. The atoms are chemically bonded, not simply mixed. This is why water has properties different from both hydrogen gas and oxygen gas. The subscript \(2\) belongs to hydrogen, so each molecule contains two hydrogen atoms for one oxygen atom. A chemical formula gives composition at the particle level for a molecular substance.
10. A substance contains only \(\mathrm{O_2}\) particles. The most suitable classification is
ⓐ. ionic compound
ⓑ. compound of oxygen and hydrogen
ⓒ. molecule of an element
ⓓ. mixture of two unrelated gases
Correct Answer: molecule of an element
Explanation: \(\mathrm{O_2}\) consists of two oxygen atoms bonded together. Since only one element, oxygen, is present, it is not a compound. It is still a molecule because two atoms are chemically bonded as one particle. A compound must contain atoms of at least two different elements. This distinction prevents the mistaken idea that every molecule must be a compound.
11. An atom becomes an ion when it
ⓐ. shares electrons without any net charge change
ⓑ. changes physical state without changing charge
ⓒ. forms a neutral molecule without charge separation
ⓓ. loses or gains electrons
Correct Answer: loses or gains electrons
Explanation: An ion is a charged species formed when an atom or group of atoms loses or gains electrons. Loss of electrons gives a positive charge, while gain of electrons gives a negative charge. Changing only the number of neutrons gives an isotope, not an ion. A physical change of state also does not create an ion by itself. Charge formation is controlled by electron transfer because electrons carry negative charge.
12. A species with more protons than electrons will be a
ⓐ. anion
ⓑ. neutral molecule
ⓒ. cation
ⓓ. lone pair
Correct Answer: cation
Explanation: A cation is positively charged. If a species has more protons than electrons, the positive charge from protons is greater than the negative charge from electrons. This usually happens when an atom loses one or more electrons. An anion has excess electrons and therefore carries a negative charge. The names cation and anion should be linked with charge sign, not with size or mass.
13. Use the table below to identify the row that gives the best description of each species.
| Row | Species | Description |
|---|
| P | \(\mathrm{Na^+}\) | cation formed by loss of an electron |
| Q | \(\mathrm{Cl^-}\) | anion formed by gain of an electron |
| R | \(\mathrm{O_2}\) | molecule of an element |
| S | \(\mathrm{CO_2}\) | compound containing two elements |
The set of descriptions that fits the basic bonding vocabulary is
ⓐ. P, Q, R, and S
ⓑ. P and Q only
ⓒ. R and S only
ⓓ. P, Q, and R only
Correct Answer: P, Q, R, and S
Explanation: \(\mathrm{Na^+}\) is a cation because sodium has lost an electron and gained a positive charge. \(\mathrm{Cl^-}\) is an anion because chlorine has gained an electron and carries a negative charge. \(\mathrm{O_2}\) is a molecule of an element because both atoms are oxygen. \(\mathrm{CO_2}\) is a compound because it contains carbon and oxygen chemically combined. These four descriptions use different vocabulary terms, so no single label can replace all of them.
14. In a simple comparison, electron transfer is most closely associated with ionic bonding, while electron sharing is most closely associated with
ⓐ. nuclear fission
ⓑ. isotope formation
ⓒ. covalent bonding
ⓓ. physical adsorption only
Correct Answer: covalent bonding
Explanation: Ionic bonding begins with transfer of electrons, usually from a metal atom to a non-metal atom. Covalent bonding involves sharing of electron pairs between atoms. Both processes can help atoms reach a more stable arrangement, but the electron behaviour is different. Electron sharing does not automatically mean ions are formed. This distinction is the starting point for separating ionic compounds such as \(\mathrm{NaCl}\) from covalent molecules such as \(\mathrm{Cl_2}\).
15. Use the arrangement described below. In a water molecule, oxygen is bonded to two hydrogen atoms and still has two pairs of electrons not used in bonding. The electron pairs not used in bonding are called
ⓐ. lone pairs
ⓑ. bond pairs
ⓒ. cations
ⓓ. double bonds
Correct Answer: lone pairs
Explanation: A lone pair is an electron pair present on an atom but not shared between two atoms as a bond. In \(\mathrm{H_2O}\), oxygen forms two \(\mathrm{O-H}\) bonds and also keeps two lone pairs. A bond pair lies between bonded atoms and contributes to the bond. Lone pairs are important because they affect molecular shape and bond angle. The term does not mean that the electrons are absent; it means they are non-bonding pairs on an atom.
16. Match each bond description with the number of shared electron pairs.
| Bond description | Number of shared electron pairs |
|---|
| P. Single bond | \(1\) |
| Q. Double bond | \(2\) |
| R. Triple bond | \(3\) |
The suitable matching is
ⓐ. P-\(2\), Q-\(1\), R-\(3\)
ⓑ. P-\(1\), Q-\(3\), R-\(2\)
ⓒ. P-\(3\), Q-\(2\), R-\(1\)
ⓓ. P-\(1\), Q-\(2\), R-\(3\)
Correct Answer: P-\(1\), Q-\(2\), R-\(3\)
Explanation: A single bond contains one shared electron pair. A double bond contains two shared electron pairs. A triple bond contains three shared electron pairs. This count is a basic way to connect Lewis structures with bond order. The number of lines in simple structural formulas such as \(\mathrm{H-H}\), \(\mathrm{O=O}\), and \(\mathrm{N\equiv N}\) represents the number of shared pairs.
17. Consider these statements about molecules and compounds.
I. Every compound contains atoms of at least two different elements.
II. Every molecule must contain atoms of at least two different elements.
III. \(\mathrm{O_2}\) is a molecule but not a compound.
The valid combination is
ⓐ. I only
ⓑ. I and III only
ⓒ. II and III only
ⓓ. I, II, and III
Correct Answer: I and III only
Explanation: A compound must contain two or more different elements chemically combined. A molecule, however, may contain atoms of the same element or of different elements. \(\mathrm{O_2}\) is a molecule because two oxygen atoms are bonded, but it is not a compound because only oxygen is present. Statement II is too broad and gives a wrong condition for all molecules. The pair \(\mathrm{O_2}\) and \(\mathrm{CO_2}\) is useful for keeping molecule and compound separate.
18. When a chlorine atom gains one electron during ion formation, the resulting species is represented as
ⓐ. \(\mathrm{Cl^+}\)
ⓑ. \(\mathrm{Cl^-}\)
ⓒ. \(\mathrm{Cl_2}\)
ⓓ. \(\mathrm{Cl}\)
Correct Answer: \(\mathrm{Cl^-}\)
Explanation: An electron has negative charge. When chlorine gains one electron, it has one more electron than protons, so the species becomes negatively charged. The symbol \(\mathrm{Cl^-}\) represents a chloride ion. \(\mathrm{Cl^+}\) would correspond to loss of an electron, not gain. \(\mathrm{Cl_2}\) is a neutral molecule formed by sharing electrons between two chlorine atoms, so it is not the same as a chloride ion.
19. A note describes a particle as follows: it contains one carbon atom and two oxygen atoms chemically bonded together. The notation that best represents this particle is
ⓐ. \(\mathrm{CO_2}\)
ⓑ. \(\mathrm{CO}\)
ⓒ. \(\mathrm{C_2O}\)
ⓓ. \(\mathrm{O_2}\)
Correct Answer: \(\mathrm{CO_2}\)
Explanation: The formula must show one carbon atom and two oxygen atoms in the same particle. \(\mathrm{CO_2}\) has no subscript after carbon, so it contains one carbon atom, and the subscript \(2\) after oxygen shows two oxygen atoms. \(\mathrm{CO}\) has only one oxygen atom. \(\mathrm{C_2O}\) reverses the count by giving two carbon atoms and one oxygen atom. Subscripts in chemical formulas apply to the symbol immediately before them.
20. The pair of terms that describes shared and non-shared electron pairs in bonding is
ⓐ. bond pair and lone pair
ⓑ. cation and anion
ⓒ. valence shell and nucleus
ⓓ. molecule and compound
Correct Answer: bond pair and lone pair
Explanation: A bond pair is an electron pair shared between two bonded atoms. A lone pair is an electron pair present on an atom but not shared as a bond. Cation and anion describe charged species, not electron-pair roles. Molecule and compound describe types of chemical species, while valence shell describes the outermost occupied electron shell. The bond-pair and lone-pair distinction is especially useful when predicting molecular shapes.
Discussing about Que no:
1. Which statement best describes a chemical bond?
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