1. The main reason for studying the structure of the atom is that it helps explain
ⓐ. charge, mass, spectra, and reactivity
ⓑ. colour and physical appearance of substances
ⓒ. element names, symbols, and formula writing
ⓓ. the shape of laboratory glassware
Correct Answer: charge, mass, spectra, and reactivity
Explanation: Modern chemistry does not treat the atom as a featureless indivisible sphere. The internal arrangement of charged and massive particles helps explain why atoms form ions, why atoms have mass, and why elements show characteristic spectra. Chemical behaviour also depends on the arrangement of electrons around the nucleus. Atomic structure is studied because properties of matter cannot be fully understood by only naming atoms and molecules. A narrow idea such as colour alone misses the wider role of atomic structure in explaining both physical and chemical properties.
2. A description says, "An atom is the smallest unit that takes part in ordinary chemical changes, but it has its own internal structure." This statement mainly rejects the older idea that atoms are
ⓐ. electrically neutral in all situations
ⓑ. completely indivisible particles
ⓒ. made only during chemical reactions
ⓓ. heavier than all molecules
Correct Answer: completely indivisible particles
Explanation: The statement keeps the useful chemical idea that atoms are basic units in reactions, but it adds the modern idea that atoms contain smaller particles. Discovery of electrons, protons, and neutrons showed that atoms have internal structure. An atom may be neutral as a whole, but that does not mean it has no charged parts inside it. Molecules are made of atoms, so comparing atom and molecule masses is not the central issue here. The key shift is from "indivisible atom" to "atom with internal charged and massive constituents."
3. Match the particle in Column I with its usual basic description in Column II.
| Column I | Column II |
|---|
| P. Electron | 1. Neutral subatomic particle |
| Q. Proton | 2. Negatively charged subatomic particle |
| R. Neutron | 3. Positively charged subatomic particle |
ⓐ. P-1, Q-2, R-3
ⓑ. P-3, Q-1, R-2
ⓒ. P-2, Q-1, R-3
ⓓ. P-2, Q-3, R-1
Correct Answer: P-2, Q-3, R-1
Explanation: An electron is the negatively charged subatomic particle and is represented as \(e^-\). A proton carries positive charge and is represented as \(p^+\). A neutron has no charge and is represented as \(n^0\). These three particles form the basic vocabulary of atomic structure. The notation signs are not decoration; they show whether the particle contributes negative charge, positive charge, or no charge.
4. The notation row below is meant to summarize the charge sign of the three main subatomic particles. Identify the row that is fully consistent.
| Row | Electron | Proton | Neutron |
|---|
| P | \(e^-\) | \(p^+\) | \(n^0\) |
| Q | \(e^+\) | \(p^-\) | \(n^0\) |
| R | \(e^-\) | \(p^0\) | \(n^+\) |
| S | \(e^0\) | \(p^+\) | \(n^-\) |
ⓐ. Row P
ⓑ. Row Q
ⓒ. Row R
ⓓ. Row S
Correct Answer: Row P
Explanation: The electron is written as \(e^-\) because it carries negative charge. The proton is written as \(p^+\) because it carries positive charge. The neutron is written as \(n^0\) because it has no charge. Changing only the superscript changes the physical meaning of the particle notation. The safest way to read the symbols is to connect \(e^-\) with negative, \(p^+\) with positive, and \(n^0\) with neutral.
5. A neutral atom contains \(12\) protons in its nucleus. The number of electrons present in the atom is
ⓐ. \(0\)
ⓑ. \(12\)
ⓒ. \(6\)
ⓓ. \(24\)
Correct Answer: \(12\)
Explanation: A neutral atom has no net electrical charge. Since each proton contributes one positive relative charge, \(12\) protons contribute \(+12\) relative charge. To balance this, the atom must contain \(12\) electrons, each with relative charge \(-1\). Neutrons do not affect the charge balance because their relative charge is \(0\). Neutrality depends on equality of proton count and electron count, not on the total number of particles in the atom.
6. Use the arrangement described below: a tiny central region contains protons and neutrons, while electrons are present outside this region. The central region is called the
ⓐ. valence shell
ⓑ. molecule
ⓒ. nucleus
ⓓ. electron cloud only
Correct Answer: nucleus
Explanation: The nucleus is the small central part of an atom that contains protons and neutrons. Electrons occupy the extranuclear region around the nucleus. The word "valence shell" refers to the outermost electron shell, not to the central positive part of the atom. A molecule is made when atoms combine, so it is not the internal central region of one atom. This vocabulary is important because later atomic models discuss the nucleus and electrons separately.
7. For comparing the masses of the basic subatomic particles, the most suitable statement is that
ⓐ. an electron is much lighter than a proton or a neutron
ⓑ. a proton is nearly massless compared with an electron
ⓒ. a neutron has exactly zero mass because it has zero charge
ⓓ. all three particles have equal mass because they are subatomic
Correct Answer: an electron is much lighter than a proton or a neutron
Explanation: The electron has a very small mass compared with a proton or a neutron. Proton and neutron masses are close to each other on the relative mass scale used in basic atomic structure. A neutron is neutral in charge, but neutrality does not mean absence of mass. Equal subatomic status also does not imply equal mass. This distinction prepares the idea that most atomic mass is associated with the nucleus, while electrons mainly determine charge balance and chemical behaviour.
8. A claim says, "Because an atom is electrically neutral, it cannot contain charged particles." The best response is that
ⓐ. neutrality means the atom contains only neutrons
ⓑ. opposite charges balance in a neutral atom
ⓒ. charged particles are present only outside atoms
ⓓ. electrons and protons have no charge inside an atom
Correct Answer: opposite charges balance in a neutral atom
Explanation: Electrical neutrality of the whole atom does not require every internal particle to be neutral. A neutral atom contains positively charged protons and negatively charged electrons in equal numbers. Their charges cancel when the atom is considered as a complete unit. Neutrons contribute mass but no charge to this balance. The mistake in the claim is confusing "net charge is zero" with "no charged particles are present."
9. The central idea of internal atomic structure is best expressed as
ⓐ. atoms are made only of protons
ⓑ. atoms have no role in chemical behaviour
ⓒ. subatomic particles arranged in distinct regions
ⓓ. electrons are found inside the nucleus with neutrons
Correct Answer: subatomic particles arranged in distinct regions
Explanation: Atomic structure deals with the particles inside an atom and their arrangement. Protons and neutrons are associated with the nucleus, while electrons are in the region outside the nucleus. This internal arrangement helps explain charge, mass, and later chemical properties. Saying that atoms contain only protons ignores electrons and neutrons. The phrase "distinct regions" is useful because atomic models are built around the separation between nucleus and extranuclear electrons.
10. A neutral atom has atomic number \(Z=8\). Its electron count is
ⓐ. \(4\)
ⓑ. \(16\)
ⓒ. \(0\)
ⓓ. \(8\)
Correct Answer: \(8\)
Explanation: \( \textbf{Given information:} \) The atom is neutral and has \(Z=8\).
\( \textbf{Meaning of } Z\textbf{:} \) Atomic number \(Z\) gives the number of protons.
\( \textbf{Protons present:} \) Number of protons \(=8\).
\( \textbf{Neutrality condition:} \) In a neutral atom, number of electrons equals number of protons.
\( \textbf{Electron count:} \)
\[
\text{electrons}=8
\]
\( \textbf{Charge check:} \) \(8\) protons give \(+8\) relative charge and \(8\) electrons give \(-8\) relative charge.
\( \textbf{Net charge:} \) \(+8+(-8)=0\).
\( \textbf{Final answer:} \) The neutral atom contains \(8\) electrons. Choosing \(16\) would wrongly double \(Z\) instead of using it directly as the proton count.
11. Two statements about subatomic particles are given.
Statement I: A proton and an electron have equal magnitude of charge but opposite signs.
Statement II: A neutron has zero charge but a mass close to that of a proton.
ⓐ. Statement I is true, but Statement II is false
ⓑ. Statement I is false, but Statement II is true
ⓒ. Both Statement I and Statement II are false
ⓓ. Both Statement I and Statement II are true
Correct Answer: Both Statement I and Statement II are true
Explanation: The proton carries positive charge and the electron carries negative charge of equal basic magnitude. In relative charge terms, proton is \(+1\) and electron is \(-1\). A neutron is electrically neutral, so its relative charge is \(0\). However, zero charge does not mean zero mass; neutron mass is close to proton mass. The two statements test different properties, so charge sign and mass comparison must be read separately.
12. In the symbol \(n^0\), the superscript \(0\) shows that the particle
ⓐ. has zero charge
ⓑ. has no mass
ⓒ. is outside every atom
ⓓ. has positive charge
Correct Answer: has zero charge
Explanation: The symbol \(n^0\) represents a neutron. The superscript \(0\) is used to show that the neutron has no electrical charge. This does not mean that the neutron has no mass; neutron mass is close to proton mass. The symbols \(e^-\) and \(p^+\) show negative and positive charge respectively. Reading the superscript as charge avoids mixing up neutrality with absence of matter.
13. A subatomic particle has relative charge \(+1\) and mass close to \(1\,u\). The particle is a
ⓐ. neutron
ⓑ. molecule
ⓒ. electron
ⓓ. proton
Correct Answer: proton
Explanation: A proton has relative charge \(+1\) and a mass close to \(1\,u\) on the simple relative mass scale. A neutron also has mass close to \(1\,u\), but its relative charge is \(0\). An electron has relative charge \(-1\), but its mass is much smaller than \(1\,u\). A molecule is not a subatomic particle, so it does not belong to the same category as electron, proton, and neutron. The charge sign is the deciding clue between proton and neutron in this question.
14. Use the data record below for a neutral atom.
Protons: \(6\)
Electrons: \(6\)
Neutrons: \(8\)
The net relative charge of this atom is
ⓐ. \(0\)
ⓑ. \(+6\)
ⓒ. \(-6\)
ⓓ. \(+8\)
Correct Answer: \(0\)
Explanation: \( \textbf{Given particles:} \) Protons \(=6\), electrons \(=6\), neutrons \(=8\).
\( \textbf{Relative charge values:} \) Proton \(=+1\), electron \(=-1\), neutron \(=0\).
\( \textbf{Charge from protons:} \)
\[
6\times(+1)=+6
\]
\( \textbf{Charge from electrons:} \)
\[
6\times(-1)=-6
\]
\( \textbf{Charge from neutrons:} \)
\[
8\times0=0
\]
\( \textbf{Total relative charge:} \)
\[
+6+(-6)+0=0
\]
\( \textbf{Final answer:} \) The atom has net relative charge \(0\). The \(8\) neutrons increase the particle count and mass contribution, but they do not change the electrical charge.
15. A model of the atom that ignores electrons would fail first in explaining
ⓐ. why substances occupy volume and show density
ⓑ. ion formation and charge-linked reactivity
ⓒ. why laboratory balances compare masses
ⓓ. why glass tubes tolerate heating in a flame
Correct Answer: ion formation and charge-linked reactivity
Explanation: Electrons are essential for understanding the charge behaviour of atoms and the formation of ions. Chemical behaviour is strongly connected with the arrangement and transfer or sharing of electrons. A model without electrons cannot properly explain how a neutral atom becomes charged or why different atoms behave differently in reactions. General facts such as a solid occupying space or a balance comparing masses do not specifically require the electron picture. The most direct failure is in explaining charge-related and chemical behaviour of atoms.
16. In an atom, the extranuclear region is most closely associated with
ⓐ. only neutrons
ⓑ. protons and neutrons together
ⓒ. electrons outside the nucleus
ⓓ. the total mass number only
Correct Answer: electrons outside the nucleus
Explanation: The word "extranuclear" means outside the nucleus. Electrons are associated with this region in the basic description of atomic structure. Protons and neutrons are nuclear particles, so they belong to the central nucleus rather than the extranuclear region. Mass number is a count of protons and neutrons and is not the name of a spatial region. Keeping this distinction clear helps when later models describe a small nucleus surrounded by electrons.
17. A neutral atom contains \(9\) protons, \(10\) neutrons, and \(9\) electrons. The particle that does not affect its net charge is the
ⓐ. proton
ⓑ. neutron
ⓒ. electron
ⓓ. nucleus
Correct Answer: neutron
Explanation: A neutron has relative charge \(0\), so it does not add positive or negative charge to the atom. Protons contribute positive charge, and electrons contribute negative charge. In the given atom, \(9\) protons and \(9\) electrons balance each other electrically. The \(10\) neutrons affect the mass contribution of the atom but not its charge. This is why neutron number can change in isotopes without directly changing the charge of a neutral atom.
18. The approximate relative mass pattern of the three basic subatomic particles is best represented by
ⓐ. electron \(\approx1\), proton \(\approx1\), neutron \(\approx0\)
ⓑ. electron \(\approx1\), proton \(\approx0\), neutron \(\approx1\)
ⓒ. electron \(\approx0\), proton \(\approx0\), neutron \(\approx0\)
ⓓ. electron \(\approx0\), proton \(\approx1\), neutron \(\approx1\)
Correct Answer: electron \(\approx0\), proton \(\approx1\), neutron \(\approx1\)
Explanation: On a simple relative mass scale, the electron is treated as nearly \(0\) because it is much lighter than a proton or neutron. A proton has relative mass close to \(1\), and a neutron also has relative mass close to \(1\). This does not mean the electron has exactly zero mass; it means its mass is very small compared with nuclear particles. The proton and neutron are the main contributors to atomic mass. The charge of a particle and its mass should not be mixed while comparing these particles.
19. A record of a neutral particle system is shown below.
| Case | Protons | Electrons | Neutrons |
|---|
| P | \(5\) | \(5\) | \(6\) |
| Q | \(5\) | \(4\) | \(6\) |
| R | \(5\) | \(6\) | \(6\) |
| S | \(5\) | \(5\) | \(0\) |
For the same number of protons, the cases that are electrically neutral are
ⓐ. Q and R only
ⓑ. P, Q, and S only
ⓒ. P and S only
ⓓ. P, R, and S only
Correct Answer: P and S only
Explanation: A neutral atom or particle system has equal numbers of protons and electrons. In Case P, \(5\) protons are balanced by \(5\) electrons, so the net charge is zero. In Case S, the same charge balance exists even though no neutron is listed. Case Q has fewer electrons than protons, so it is positively charged, and Case R has more electrons than protons, so it is negatively charged. Neutrons can change the mass-related count, but equality of protons and electrons decides neutrality.
20. The symbol \(e^-\) is more informative than simply writing "electron" because it directly shows the particle's
ⓐ. mass number
ⓑ. nuclear position
ⓒ. negative charge
ⓓ. neutron count
Correct Answer: negative charge
Explanation: The superscript minus sign in \(e^-\) indicates that an electron carries negative charge. It does not show mass number, because mass number is used for atoms or nuclei and counts nucleons. The electron is not a nuclear particle in the basic atomic-structure picture. Neutron count is also unrelated to the electron symbol. The notation is useful because it keeps the charge sign visible whenever particles are compared.
