This Elements and Compounds Test 2 is designed to help you strengthen your understanding of atoms, molecules, and basic atomic structure for TNPSC Chemistry preparation. In this test, you will revise important concepts such as protons, neutrons and electrons, atomic number, mass number, isotopes, molecules and ions. The questions also help you understand how these particles are arranged within an atom and how atoms form molecules and ions. If you have already completed Test 1, this TNPSC Chemistry quiz provides a useful continuation of your revision on Elements and Compounds, with greater focus on Atoms, Molecules, and Atomic Structure.
Note: Once you complete the test, go through the detailed explanations below to understand the answers and improve your preparation.
Elements and Compounds Test 2 : Questions With Answers – Learn, Revise & Practice
This section provides a clear explanation of the answers in Elements and Compounds – Test 2. It helps you revise the important concepts covered in the test, including atoms and molecules, protons, neutrons and electrons, atomic number, mass number, isotopes, basic atomic structure, molecules and ions. Each explanation focuses on the key idea behind the correct answer so that you can understand the concept rather than simply remember the answer. Use this section to review your mistakes, strengthen your understanding of Atoms, Molecules and Atomic Structure, and prepare more confidently for TNPSC Chemistry questions.
1. Which particle is the smallest unit of an element that retains its chemical identity?
Correct Answer: B. Atom
An atom is the smallest unit of an element that retains the chemical identity and characteristic properties of that element. Every element is made up of atoms of that element. An atom contains a central nucleus, which consists of protons and neutrons, while electrons move around the nucleus. For example, a hydrogen atom is the basic unit of the element hydrogen.
- Molecule: A molecule consists of two or more atoms chemically bonded together and may be made of atoms of the same or different elements.
- Ion: An ion is an atom or group of atoms that carries an electric charge due to the loss or gain of electrons.
- Nucleus: The nucleus is the dense central part of an atom containing protons and neutrons.
Therefore, atom is the correct answer.
2. Which of the following is a molecule of an element?
Correct Answer: C. O₂
O₂ is a molecule of the element oxygen. It contains two oxygen atoms chemically bonded together. Since both atoms are of the same element, O₂ is called a molecule of an element. Oxygen normally exists as a diatomic molecule in its elemental form.
- H₂O: Contains hydrogen and oxygen, so it is a compound.
- CO₂: Contains carbon and oxygen, so it is a compound.
- NaCl: Contains sodium and chlorine, so it is a compound.
- O₂: Contains only oxygen atoms, so it is a molecule of an element.
Thus, O₂ is the correct answer.
3. Which subatomic particle has a positive charge?
Correct Answer: A. Proton
A proton is a positively charged subatomic particle found inside the nucleus of an atom. The number of protons in an atom determines its atomic number and identifies the element. For example, every hydrogen atom has one proton, while every carbon atom has six protons.
- Electron: Has a negative charge and is found outside the nucleus.
- Neutron: Has no electric charge and is present in the nucleus.
- Atom: An atom is the complete unit of an element, not a positively charged subatomic particle.
Therefore, the proton is the positively charged subatomic particle.
4. Which subatomic particle has no electrical charge?
Correct Answer: D. Neutron
A neutron is a subatomic particle that has no electrical charge. It is found inside the nucleus of an atom, along with positively charged protons. The number of neutrons can vary among atoms of the same element, which is the basis for the existence of isotopes.
- Proton: Has a positive charge and is present in the nucleus.
- Electron: Has a negative charge and moves around the nucleus.
- Ion: Is an atom or group of atoms carrying a positive or negative charge.
Therefore, the neutron is the correct answer.
5. Which subatomic particle has a negative charge?
Correct Answer: B. Electron
An electron is a negatively charged subatomic particle found outside the nucleus of an atom. Electrons occupy different energy levels or shells around the nucleus. When an atom loses or gains electrons, it can become an ion.
- Proton: Has a positive charge and is found in the nucleus.
- Neutron: Has no electrical charge and is found in the nucleus.
- Nucleus: Is the central part of an atom containing protons and neutrons.
Thus, the electron is the negatively charged subatomic particle.
6. The nucleus of an atom contains
Correct Answer: A. Protons and neutrons
The nucleus is the small, dense central region of an atom. It contains protons and neutrons, which together are called nucleons. Protons carry a positive charge, while neutrons have no electrical charge. Almost all the mass of an atom is concentrated in its nucleus.
Electrons are not present inside the nucleus; they occupy regions or shells around the nucleus.
Therefore, the nucleus contains protons and neutrons.
7. The atomic number of an element is equal to the number of
Correct Answer: B. Protons
The atomic number of an element is defined as the number of protons present in the nucleus of an atom. It is a unique property of an element and determines its identity. For example, hydrogen has one proton, so its atomic number is 1, while carbon has six protons, giving it an atomic number of 6.
In a neutral atom, the number of electrons is also equal to the number of protons. However, the atomic number is specifically determined by the number of protons.
Therefore, protons are the correct answer.
8. An electrically neutral atom has equal numbers of
Correct Answer: C. Protons and electrons
An electrically neutral atom has no overall electrical charge. This is because the positive charge of its protons is balanced by the negative charge of its electrons. Therefore, a neutral atom has an equal number of protons and electrons. The number of neutrons does not affect the electrical charge of an atom because neutrons have no charge.
For example, if an atom has 6 protons, a neutral atom will also have 6 electrons.
Therefore, protons and electrons are equal in number in an electrically neutral atom.
9. The mass number of an atom is the total number of
Correct Answer: C. Protons and neutrons
The mass number represents the total number of protons and neutrons present in the nucleus of an atom. Protons and neutrons together are called nucleons. Electrons are not included in the mass number because their mass is extremely small compared with that of protons and neutrons.
The formula is:
Mass number = Number of protons + Number of neutrons
Therefore, the mass number is the total number of protons and neutrons.
10. An atom has 11 protons and 12 neutrons. What is its mass number?
Correct Answer: C. 23
The mass number is calculated by adding the number of protons and neutrons present in the nucleus.
Mass number = Protons + Neutrons
= 11 + 12
= 23
Electrons are not included when calculating the mass number.
Therefore, the mass number of the atom is 23.
11. An atom has atomic number 8. How many protons does it contain?
Correct Answer: A. 8
The atomic number of an element is equal to the number of protons present in the nucleus of its atom. Therefore, if an atom has an atomic number of 8, it contains 8 protons.
An atomic number uniquely identifies an element. An atom with 8 protons is an atom of oxygen.
Therefore, the atom contains 8 protons.
12. An electrically neutral atom has 17 electrons. What is its atomic number?
Correct Answer: B. 17
In an electrically neutral atom, the number of protons is equal to the number of electrons. Since the atom has 17 electrons, it must also have 17 protons.
The atomic number is equal to the number of protons.
Atomic number = Number of protons = 17
Therefore, the atomic number of the atom is 17.
13. Atoms of the same element having the same atomic number but different mass numbers are called
Correct Answer: C. Isotopes
Isotopes are atoms of the same element that have the same atomic number but different mass numbers. Since the atomic number represents the number of protons, isotopes have the same number of protons. However, they contain different numbers of neutrons, which results in different mass numbers.
For example, carbon-12 and carbon-14 are isotopes of carbon. Both have 6 protons, but carbon-12 has 6 neutrons while carbon-14 has 8 neutrons.
Therefore, such atoms are called isotopes.
14. Which pair represents isotopes of the same element?
Correct Answer: A. ¹²C and ¹⁴C
The symbols ¹²C and ¹⁴C represent two atoms of carbon. Both have the same atomic number because they are carbon atoms, but they have different mass numbers, 12 and 14. This difference is due to the different numbers of neutrons in their nuclei.
Carbon-12 has 6 protons and 6 neutrons, while carbon-14 has 6 protons and 8 neutrons.
Therefore, ¹²C and ¹⁴C are isotopes of the same element.
15. Isotopes of an element have the same number of
Correct Answer: B. Protons
Isotopes are atoms of the same element, so they must have the same number of protons. The number of protons determines the atomic number and identifies the element. Isotopes differ in their number of neutrons, which gives them different mass numbers.
For example, carbon-12 and carbon-14 both contain 6 protons, but they have different numbers of neutrons.
Therefore, isotopes of an element have the same number of protons.
16. When an atom loses one or more electrons, it forms a
Correct Answer: C. Positive ion
When an atom loses one or more negatively charged electrons, the number of positive protons becomes greater than the number of electrons. As a result, the atom develops an overall positive charge and becomes a positive ion, also called a cation.
For example, a sodium atom loses one electron to form a sodium ion (Na⁺).
Therefore, an atom that loses one or more electrons forms a positive ion.
17. When an atom gains one or more electrons, it forms a
Correct Answer: B. Negative ion
When an atom gains one or more negatively charged electrons, the number of electrons becomes greater than the number of positively charged protons. As a result, the atom develops an overall negative charge and forms a negative ion, also called an anion.
For example, a chlorine atom gains one electron to form a chloride ion (Cl⁻).
Therefore, an atom that gains one or more electrons forms a negative ion.
18. Which term refers to the positively charged centre of an atom?
Correct Answer: B. Nucleus
The nucleus is the dense central part of an atom. It contains positively charged protons and electrically neutral neutrons. Since the protons give the nucleus its positive charge, the nucleus is described as the positively charged centre of the atom.
Electrons are located outside the nucleus in different energy levels or shells.
Therefore, the nucleus is the positively charged centre of an atom.
19. Which statement about electrons in an atom is correct?
Correct Answer: A. They are located outside the nucleus
Electrons are negatively charged subatomic particles that are located outside the nucleus of an atom. They occupy different energy levels or shells around the nucleus. The arrangement of electrons plays an important role in the chemical behaviour of an element.
Electrons are not present inside the nucleus, and they do not directly determine the mass number. The mass number is the total number of protons and neutrons.
Therefore, electrons are located outside the nucleus.
20. An atom has 12 protons and 13 neutrons. Which statement is correct?
Correct Answer: B. Atomic number = 12, mass number = 25
The atomic number is equal to the number of protons present in the nucleus. Since the atom has 12 protons:
Atomic number = 12
The mass number is the total number of protons and neutrons:
Mass number = 12 + 13 = 25
Therefore, the correct statement is that the atomic number is 12 and the mass number is 25.
Quick Revision For This Test
- An atom is the smallest unit of an element that retains its chemical identity.
- A molecule consists of two or more atoms chemically bonded together. O₂ is a molecule of an element because it contains only oxygen atoms.
- Protons are positively charged subatomic particles found in the nucleus.
- Neutrons have no electrical charge and are found in the nucleus.
- Electrons are negatively charged particles located outside the nucleus in different energy levels or shells.
- The nucleus is the dense central part of an atom and contains protons and neutrons.
- Atomic number = Number of protons in the nucleus.
- In an electrically neutral atom, the number of protons is equal to the number of electrons.
- Mass number = Number of protons + Number of neutrons.
- Isotopes are atoms of the same element having the same atomic number but different mass numbers.
- Isotopes have the same number of protons but different numbers of neutrons.
- When an atom loses one or more electrons, it forms a positive ion or cation.
- When an atom gains one or more electrons, it forms a negative ion or anion.
- Remember: Atomic number identifies an element, while mass number represents the total number of protons and neutrons.
Further Reference Material for Atoms, Molecules & Atomic Structure
For additional reading on atomic structure, students can refer to the official NCERT Chemistry textbook chapter “Structure of Atom.” It provides useful explanations of subatomic particles, atomic number, mass number, isotopes and the basic structure of the atom.
Completing this test is a useful way to strengthen your understanding of atoms, molecules and atomic structure. If you made any mistakes, take a little time to review the explanations and revise concepts such as protons, neutrons, electrons, atomic number, mass number, isotopes and ions. Regular practice with these basic Chemistry concepts can help you build a stronger foundation for TNPSC preparation. Try the test again after revision and see how much your understanding has improved.