The Periodic Classification of Elements is an important part of TNPSC Chemistry, helping students understand how elements are arranged and how their properties vary across the periodic table. This test covers the periodic table, groups and periods, the classification of metals and non-metals, and important periodic trends. It also includes commonly tested elements and key concepts that are frequently asked in competitive examinations. Attempting this Elements and Compounds Test will help you revise these concepts, check your understanding, and strengthen your preparation for TNPSC Chemistry.
Note: After completing the test, review the detailed explanations below to reinforce your knowledge and identify areas that need more attention.
Elements and Compounds Test 4 – Periodic Classification of Elements : Core Ideas & Quick Revision
This detailed explanation section provides a clear review of the important concepts covered in Test 4 on Periodic Classification of Elements. The explanations focus on the periodic table, groups and periods, the classification of metals and non-metals, important elements, and the basic periodic trends in the properties of elements. Each question is explained in a simple and exam-oriented manner so that you can understand why the correct answer is appropriate and quickly revise the concepts that are commonly tested in TNPSC Chemistry.
1. The modern periodic table is arranged in increasing order of
Answer: B. Atomic number
Explanation:
The modern periodic table arranges elements in the increasing order of their atomic numbers. The atomic number represents the number of protons present in the nucleus of an atom. Since each element has a unique atomic number, this arrangement gives a systematic classification of elements and their properties.
The modern periodic law states that the physical and chemical properties of elements are periodic functions of their atomic numbers. This means that when elements are arranged according to increasing atomic number, similar properties appear at regular intervals.
Why the other options are incorrect:
- Atomic mass: Used in earlier attempts to classify elements, but the modern periodic table is based on atomic number.
- Mass number: Represents the total number of protons and neutrons in an atom and is not used to arrange the periodic table.
- Number of neutrons: Can vary among isotopes of the same element and therefore cannot be used for periodic classification.
Point: Modern periodic table → Increasing atomic number
2. How many groups are present in the modern periodic table?
Answer: C. 18
Explanation:
The modern periodic table contains 18 vertical columns, which are called groups. Elements belonging to the same group generally have similar chemical properties because they have similar arrangements of valence electrons.
The groups are numbered from 1 to 18. For example, Group 1 contains the alkali metals, Group 17 contains the halogens, and Group 18 contains the noble gases.
Groups help us understand the similarities in the chemical behaviour of elements and are therefore an important part of the modern periodic classification.
Why the other options are incorrect:
- 7: The modern periodic table has 7 periods, not groups.
- 8: This was associated with older classifications and does not represent the number of groups in the modern periodic table.
- 32: This is not the number of groups in the modern periodic table.
Point: Modern periodic table → 18 groups → Vertical columns
3. How many periods are present in the modern periodic table?
Answer: B. 7
Explanation:
The modern periodic table contains 7 horizontal rows, which are called periods. The periods are numbered from 1 to 7. As we move from left to right across a period, the atomic number of the elements generally increases by one.
The period number is related to the number of electron shells occupied in the atoms of the elements in that period. For example, elements in the first period have only one occupied electron shell, while elements in the second period have two occupied electron shells.
The seven periods contain different numbers of elements, with the first period containing 2 elements and the sixth and seventh periods containing 32 elements each.
Why the other options are incorrect:
- 6: The modern periodic table has 7 periods.
- 8: There are no 8 periods in the modern periodic table.
- 18: 18 represents the number of groups, not periods.
Point: 👉 Modern periodic table → 7 periods → Horizontal rows
4. Elements in the same group generally have similar
Answer: B. Chemical properties
Explanation:
Elements in the same group of the modern periodic table generally have similar chemical properties because they have a similar arrangement of valence electrons. The valence electrons are the electrons present in the outermost shell of an atom and they play an important role in determining how an element reacts chemically.
For example, lithium, sodium, and potassium are all placed in Group 1 and show similar chemical behaviour because each has one valence electron.
Why the other options are incorrect:
- Atomic masses: Elements in the same group do not necessarily have similar atomic masses.
- Number of neutrons: The number of neutrons varies among different elements and their isotopes.
- Mass numbers: Mass numbers are different for different elements and isotopes.
Point: Same group → Similar valence electrons → Similar chemical properties
5. Which group contains the alkali metals?
Answer: A. Group 1
Explanation:
The alkali metals are placed in Group 1 of the modern periodic table. This group includes lithium, sodium, potassium, rubidium, caesium, and francium. They are highly reactive metals and generally have one electron in their outermost shell.
Alkali metals readily lose this one valence electron to form +1 ions. Their reactivity generally increases as we move down the group.
Why the other options are incorrect:
- Group 2: Contains the alkaline earth metals.
- Group 17: Contains the halogens.
- Group 18: Contains the noble gases.
Point: Group 1 → Alkali metals → 1 valence electron
6. Which group contains the alkaline earth metals?
Answer: B. Group 2
Explanation:
The alkaline earth metals are placed in Group 2 of the modern periodic table. This group includes beryllium, magnesium, calcium, strontium, barium, and radium.
These elements generally have two valence electrons and tend to lose both electrons to form +2 ions. They are reactive metals, although generally less reactive than the alkali metals of Group 1.
Why the other options are incorrect:
- Group 1: Contains the alkali metals.
- Group 16: Contains the oxygen family or chalcogens.
- Group 17: Contains the halogens.
Point: Group 2 → Alkaline earth metals → 2 valence electrons
7. Which group contains the halogens?
Answer: C. Group 17
Explanation:
The halogens are placed in Group 17 of the modern periodic table. The group includes fluorine, chlorine, bromine, iodine, and astatine. Halogens are highly reactive non-metals and generally have seven valence electrons.
They tend to gain one electron to complete their outermost shell and usually form −1 ions. Halogens readily react with metals to form compounds known as halides.
Why the other options are incorrect:
- Group 1: Contains the alkali metals.
- Group 2: Contains the alkaline earth metals.
- Group 18: Contains the noble gases.
Point: Group 17 → Halogens → 7 valence electrons
8. Which group contains the noble gases?
Answer: D. Group 18
Explanation:
The noble gases are placed in Group 18 of the modern periodic table. This group includes helium, neon, argon, krypton, xenon, and radon.
Noble gases are generally chemically unreactive because their outermost electron shells are completely filled. Helium has two electrons in its only shell, while the other noble gases generally have eight valence electrons.
Why the other options are incorrect:
- Group 1: Contains the alkali metals.
- Group 14: Contains the carbon family.
- Group 17: Contains the halogens.
Point: Group 18 → Noble gases → Completely filled outer shell
9. Which element belongs to the halogen group?
Answer: B. Chlorine
Explanation:
Chlorine (Cl) belongs to the halogen group, which is Group 17 of the modern periodic table. Halogens are highly reactive non-metals and have seven valence electrons, so they tend to gain one electron to achieve a stable electronic configuration.
The halogen group includes fluorine, chlorine, bromine, iodine, and astatine. These elements readily combine with metals to form salts; for example, chlorine reacts with sodium to form sodium chloride (NaCl).
Why the other options are incorrect:
- Sodium: It belongs to Group 1, the alkali metals.
- Calcium: It belongs to Group 2, the alkaline earth metals.
- Neon: It belongs to Group 18, the noble gases.
Point: Halogens → Group 17 → 7 valence electrons
10. Which element belongs to the noble gas group?
Answer: C. Neon
Explanation:
Neon (Ne) belongs to the noble gas group, which is Group 18 of the modern periodic table. Noble gases are generally very unreactive because their outermost electron shells are completely filled.
The noble gases include helium, neon, argon, krypton, xenon, and radon. Neon has a completely filled outer electron shell and is commonly used in neon lighting and illuminated signs.
Why the other options are incorrect:
- Oxygen: It belongs to Group 16.
- Nitrogen: It belongs to Group 15.
- Chlorine: It belongs to Group 17, the halogens.
Point: Noble gases → Group 18 → Very low chemical reactivity
11. As we move from left to right across a period, atomic radius generally
Answer: B. Decreases
Explanation:
As we move from left to right across a period, the atomic radius generally decreases. This happens because the atomic number increases, so the number of protons in the nucleus increases. The added electrons enter the same principal electron shell, while the increasing nuclear charge pulls the electrons more strongly towards the nucleus.
As a result, the size of the atom gradually becomes smaller from left to right across a period.
For example, in the second period, the atomic radius generally decreases from lithium to fluorine.
Why the other options are incorrect:
- Increases: Atomic radius generally decreases across a period.
- Remains constant: Atomic size changes as nuclear charge increases.
- First decreases then always increases: This does not describe the general periodic trend across a period.
Point: Across a period → Atomic radius generally decreases
12. As we move down a group, atomic radius generally
Answer: A. Increases
Explanation:
As we move down a group, the atomic radius generally increases. Each successive element has an additional electron shell, which increases the distance between the nucleus and the outermost electrons.
Although the nuclear charge also increases down the group, the effect of the additional electron shells and increased shielding effect causes the outer electrons to be farther from the nucleus. Therefore, the size of the atom increases.
For example, the atomic radius increases as we move down Group 1, from lithium to sodium and then to potassium.
Why the other options are incorrect:
- Decreases: Atomic radius generally increases down a group.
- Remains constant: Additional electron shells cause the atomic size to change.
- Becomes zero: Atomic radius does not become zero.
Point: Down a group → Atomic radius generally increases
13. The metallic character of elements generally decreases
Answer: A. Across a period from left to right
Explanation:
The metallic character of elements generally decreases from left to right across a period. This is because the atomic number and effective nuclear charge increase across a period, causing the nucleus to attract the outermost electrons more strongly. As a result, the tendency of an atom to lose electrons decreases, and the metallic character gradually decreases.
For example, in the third period, sodium is more metallic than magnesium, aluminium, and silicon.
Why the other options are incorrect:
- Down a group: Metallic character generally increases down a group.
- Right to left across a period: Metallic character generally increases in this direction.
- From bottom to top only: This does not represent the general periodic trend.
Point:
- Across a period → Metallic character decreases
- Down a group → Metallic character increases
14. Which element is the most metallic among the following?
Answer: A. Sodium
Explanation:
Among sodium, magnesium, aluminium, and silicon, sodium is the most metallic. All four elements belong to Period 3, and metallic character generally decreases from left to right across a period.
Sodium is located at the far left of these four elements and has one valence electron, which it can lose easily to form a positive ion (Na⁺). Therefore, it shows the strongest metallic character among the given elements.
Why the other options are incorrect:
- Magnesium: More to the right than sodium, so it has lower metallic character.
- Aluminium: Its metallic character is lower than that of sodium.
- Silicon: Located further right and has considerably less metallic character than sodium.
Point: Period 3: Na > Mg > Al > Si in metallic character
15. Which element is the most non-metallic among the following?
Answer: D. Fluorine
Explanation:
Among carbon, nitrogen, oxygen, and fluorine, fluorine is the most non-metallic element. These elements are all in Period 2, and non-metallic character generally increases from left to right across a period.
Fluorine is located furthest to the right among the given elements and has a very strong tendency to gain an electron. It is also the most electronegative element in the periodic table.
Why the other options are incorrect:
- Carbon: Located to the left of nitrogen, oxygen, and fluorine in Period 2.
- Nitrogen: Has less non-metallic character than oxygen and fluorine.
- Oxygen: Highly non-metallic, but fluorine has a greater non-metallic character.
Point: Period 2: C < N < O < F in non-metallic character
16. Which element is located in Group 1 and Period 3?
Answer: B. Sodium
Explanation:
Sodium (Na) is located in Group 1 and Period 3 of the modern periodic table. Group 1 contains the alkali metals, while Period 3 is the third horizontal row of the periodic table.
Sodium has the electronic configuration 2, 8, 1, meaning it has one electron in its outermost shell. It readily loses this electron to form a Na⁺ ion.
Why the other options are incorrect:
- Lithium: Group 1, but it belongs to Period 2.
- Potassium: Group 1, but it belongs to Period 4.
- Magnesium: Period 3, but it belongs to Group 2.
Point: Group 1 + Period 3 → Sodium (Na)
17. Which element is located in Group 17 and Period 3?
Answer: B. Chlorine
Explanation:
Chlorine (Cl) is located in Group 17 and Period 3 of the modern periodic table. Group 17 is known as the halogen group, and chlorine is one of the important halogens.
Chlorine has the electronic configuration 2, 8, 7, giving it seven valence electrons. It tends to gain one electron to achieve a stable electronic configuration and commonly forms the Cl⁻ ion.
Why the other options are incorrect:
- Fluorine: Group 17, but it belongs to Period 2.
- Bromine: Group 17, but it belongs to Period 4.
- Iodine: Group 17, but it belongs to Period 5.
Point: Group 17 + Period 3 → Chlorine (Cl)
18. Which of the following is a metalloid in the periodic table?
Answer: A. Silicon
Explanation:
Silicon (Si) is a metalloid, meaning it shows properties of both metals and non-metals. Metalloids are generally found along the zigzag or staircase line separating metals from non-metals in the periodic table. Silicon is located in Group 14 and Period 3.
Silicon is an important semiconductor and is widely used in electronic devices, computer chips, and solar cells because of its electrical properties.
Why the other options are incorrect:
- Sodium: An alkali metal belonging to Group 1.
- Chlorine: A non-metal belonging to the halogen group, Group 17.
- Calcium: An alkaline earth metal belonging to Group 2.
TNPSC Point:
👉 Silicon → Metalloid → Group 14 → Period 3
19. Which element is known for having a complete outermost electron shell and belongs to Group 18?
Answer: C. Argon
Explanation:
Argon (Ar) belongs to Group 18, the group of noble gases. It has a completely filled outermost electron shell, with the electronic configuration 2, 8, 8. This stable electronic configuration makes argon chemically very unreactive.
Noble gases generally have stable outer electron shells. Helium has two electrons in its only shell, while the other commonly studied noble gases have eight electrons in their outermost shell.
Why the other options are incorrect:
- Sodium: Has one valence electron and belongs to Group 1.
- Chlorine: Has seven valence electrons and belongs to Group 17.
- Magnesium: Has two valence electrons and belongs to Group 2.
Point: Argon → Group 18 → Noble gas → Electronic configuration 2, 8, 8
20. Which statement about periodic classification is correct?
Answer: B. Elements in a group generally show similar chemical properties
Explanation:
Elements in the same group generally show similar chemical properties because they have similar arrangements of valence electrons. Since the valence electrons largely determine how elements participate in chemical reactions, elements within a group often exhibit related chemical behaviour.
For example, sodium and potassium belong to Group 1 and both readily lose one valence electron to form +1 ions. Similarly, the elements of Group 17 show the characteristic properties of halogens.
Why the other options are incorrect:
- Elements in a period always have the same chemical properties: Elements in the same period have different properties that change gradually from left to right.
- Atomic number decreases from left to right: Atomic number increases from left to right.
- All elements in the periodic table are metals: The periodic table contains metals, non-metals, and metalloids.
Point: Same group → Similar valence electrons → Generally similar chemical properties
Further Reference For Test 4 “Periodic Classification of Elements”
For further understanding of Periodic Classification of Elements, students can refer to the NCERT Chemistry textbook chapter “Classification of Elements and Periodicity in Properties.” It provides detailed coverage of the development of the Periodic Table, Modern Periodic Law, electronic configuration, groups and periods, and periodic trends.
