5. Periodic Classification of elements SEBA/ASSEB Class 10 Science– Important Questions and Answers | Assam HSLC

SEBA/ASSEB Class 10 Science Chapter 5: Periodic Classification of elements Important Questions and Answers | HSLC Assam

Chapter 5: Periodic Classification of elements

Multiple Choice Questions and Answers:

Question: Upto which element, the Law of Octaves was found to be applicable

(a) Oxygen (b) Calcium (c) Cobalt (d) Potassium

Answer: (b) Calcium

[ The law was found to be applicable up to calcium.]

Question: According to Mendeleev's′ Periodic Law, the elements were arranged in the periodic table in the order of

(a) increasing atomic number (b) decreasing atomic number

Answer : (c) increasing atomic masses

[ Mendeleev's periodic table was based on the increasing atomic masses of elements.]

Question: Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic Table. [SEBA 2018]

(a) The elements become less metallic in nature. (b) The number of valence electrons increases.

Answer : (b) The number of valence electrons increases.

Question: Which one of the following elements exhibit maximum number of valence electrons?

(a) Na (b) Al (c) Si (d) P

Answer : (d) P

[ Na → 2.8.1 , Al → 2.8.3 , Si →2.8.4 , P → 2.8.5 ]

Question: Which among the following elements has the largest atomic radii?

(a) Na (b) Mg (c) K (d) Ca

Answer : (c) K

[ Atomic radius generally increases down a group in the periodic table. ]

Question: Arrange the following elements in the order of their decreasing metallic character : Na , Si , Cl , Mg , Al

(a) Cl > Si >Al > Mg >Na (b) Na >Mg >Al >Si > Cl

Answer : (b) Na > Mg > Al > Si > Cl

Question: Arrange the following elements in the order of their increasing non-metallic character : Li , O , C , Be , F

(a) F < O < C < Be < Li (b) Li < Be < C < O< F

Answer : (d) F < O < Be < C < Li

Question: In Mendeleev′ ’s Periodic Table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the perioidc table later

(a) Germanium (b) Chlorine (c) Oxygen (d) Silicon

Answer : (a) Germanium

[ The element that found a place in Mendeleev's Periodic Table later is germanium.]

Question: Which of the following statements about the Modern Periodic Table is correct:

(a) It has 18 horizontal rows known as Periods (b) It has 7 vertical columns known as Periods

Answer : (c) It has 18 vertical columns known as Groups.

Question : In the periodic table of the elements, in a period from left to right atomic radius gradually :[SEBA2016]

(a) increases (b) decreases (c) remain same (d) none of the above

Answer : (b) decreases.

[ In the periodic table of elements, as you move from left to right across a period, the atomic radius generally decreases. ]

Question: Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic Table. [SEBA 2018]

(a) The elements become less metallic in nature. (b) The number of valence electrons increases.

Answer: (c) The atoms lose their electrons more easily.

[From left to right across a period, the effective nuclear charge increases, so atoms hold their electrons more strongly. Therefore, it becomes more difficult for atoms to lose electrons.]

Question: Which of the given elements A, B, C, D and E with atomic number 2, 3, 7, 10 and 30 respectively belong to the same period?

(a) A, B, C (b) B, C, D (c) A, D, E (d) B, D, E

Answer : (b) B, C, D

[ These elements actually belong to the same period (period 2) in the periodic table. ]

Question: Using Mendeleev’s Periodic Table the formula predicted for the oxide of element ‘K’ is : [2021]

(a) (b) (c) (d)

Answer: (b)

[ The predicted formula for the oxide of element ‘K’ is K₂O.]

Question: In the periodic Table, which of the following properties increase from top to bottom in a group [2024]

(i) Valency (ii) Metallic character (iii) Effective nuclear charge (iv) Atomic radius

(a) (i) and (ii) (b) (ii) and (iv) (c) (iii) and (iv) (d) (i) and (iv)

Answer: (b) (ii) and (iv)

[ From top to bottom in a group, metallic character and atomic radius increase due to the addition of electron shells. Valency remains the same.]

Question: Three elements B, Si and Ge are

(a) metals (b) non-metals (c) metalloids (d) metal, non-metal and metalloid respectively

Answer : (c) metalloids .

[ The elements Boron (B), Silicon (Si), and Germanium (Ge) are metalloids. ]

Question: The elements A, B, C, D and E have atomic number 9, 11, 17, 12 and 13 respectively. Which pair of elements belong to the same group?

(a) A and B (b) B and D (c) A and C (d) D and E

Answer : (a) A and C

[ A → 2.7 , B →2.8.1 , C → 2.8.7 , D → 2.8.2 , E → 2.8.3 ]

Question: Which of the following is the outermost shell for elements of period 2?

(a) K shell (b) L shell (c) M shell (d) N shell

Answer : (b) L shell

[ In the Modern Periodic Table, elements of period 2 have electrons filling the first and second shells. The outermost shell for elements of period 2 is the second shell.]

Question : An atom has electronic configuration 2,8,7 . To which of the following elements would it be chemically, similar ?

(atomic numbers are given in the parentheses ) [SEBA 2017,2020]

(a) N(7) (b) F(9) (c) P(15) (d) Ar(18)

Answer : (b) F(9)

[Electronic configuration of N is 2.5

Electronic configuration of F is 2.7

Electronic configuration of P is 2.8.5

Electronic configuration of Ar is 2.8.8 ]

Question : Which of the following is not an example of metalloid ? [2023]

(a) Si (b) Ge (c) B (d) Al

Answer : (d) Al

Question: What can be the maximum number of sulphur atoms present in a molecule ? [2024]

(a) 2 (b) 4 (c) 8 (d) 10

Answer: (c) 8

[ Sulphur can form an molecule, containing eight sulphur atoms arranged in a ring.]

Question: Element X forms a chloride with the formula , which is a solid with high melting point. X would most likely be in same group of the periodic Table as [2019, 2024]

(a) Na (b) Mg (c) Al (d) Si

Answer: (b) Mg

[ X forms XCl₂, indicating a valency of 2. Magnesium belongs to Group 2 and forms an ionic chloride with a high melting point.]

Question: By considering their position in the periodic table, which one of the following elements would you expect to have maximum metallic characteristic ? [2025]

(a) Ga (b) Ge (c) As (d) Se

Answer: (a) Ga

[ Metallic character decreases from left to right across a period. Gallium (Ga) is the leftmost element among the given options, so it has the maximum metallic character.]

Question: Boron is a non-metal and is placed under group 13 and period 2 of the periodic table . How can boron form bonds with other elements ? [2025]

(a) By sharing 5 electrons (b) By sharing 3 electrons (c) By sharing 2 electrons (d) By sharing 1 electron

Answer: (b) By sharing 3 electrons

[ Boron has three valence electrons and forms covalent bonds by sharing these three electrons with other atoms.]

Question: What is the trend of valency along the periods in the modern periodic table ? [2025]

(a) It increases from left to right (b) It decreases from right to left

Answer: (c) It increases and then decreases

[ Across a period, valency increases from 1 to 4 and then decreases to 0 as the number of valence electrons increases from left to right.]

Long Answer Questions and Answers ( From 1 Mark to 2 Marks):

Question: What was basis of arrangement of elements in Mendeleev’s Period Table ? Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? [2021]

Answer: Mendeleev arranged the elements in increasing order of their atomic masses and according to their chemical properties.

Besides gallium, two elements that were discovered later and had been left as gaps in Mendeléev’s Periodic Table are germanium (Ge) and scandium (Sc) .

Question: Identify and name the metals out of the following elements whose electronic configurations are given below.

(a) 2, 8, 2 (b) 2, 8, 1 (c) 2, 8, 7 (d) 2, 1

Answer : (a) Metal: Magnesium (Mg) - 2.8.2

(b) Metal: Sodium (Na) – 2.8.1

(d) Metal: Lithium (Li) – 2.1

Question: Why do you think the noble gases are placed in a separate group? [SEBA 2018]

Answer: Noble gases are placed in a separate group because their valency is zero. They have a completely filled outermost shell, so they are very stable and do not easily react with other elements. Therefore, they are placed separately in Group 18 of the Modern Periodic Table.

Question: What were the criteria used by Mendeleev in creating his Periodic Table ?

Answer: Mendeleev used the relationship between the atomic masses of the elements and their physical and comical properties .The formulae of the hydrides and oxides formed by an element were treated as one of the basic properties of an element for its classification .

Question: Why do you think the noble gases are placed in a separate group ?

Answer: The noble gases are very inert and present in extremely low concentrations in our atmosphere .When the noble gases were discovered , they could be places in a new group without disturbing the existing order . So, the noble gases are placed in a separate group .

Question: What is the valency of magnesium with atomic number 12 and sulphur with atomic number 16 ?

Answer: Atomic number of magnesium is 12 .

The electron configuration of Mg is 2.8.2 .

So, the valency of Mg is 2 .

The atomic number of sulphur is 16 .

The electron configuration of S is 2.8.6 .

So, the valency of S is 2 (= 8 – 6 ).

Question: (a) What property do all elements in the same column of the Periodic Table as boron have in common?

(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?

Answer: (a) All the elements in the same column as boron belong to Group 13 and have three electrons in their outermost shell.

(b) All the elements in the same column as fluorine belong to Group 17 and have seven electrons in their outermost shell.

Question: Name :

(a) three elements that have a single electron in their outermost shells .

(b) two elements that have two electrons in their outermost shells .

Answer:

Electronic configuration

Atomic numbers

Name of elements

(a)

2.1

2.8.1

2.8.8.1

Lithium

Sodium

Potassium

(b)

2.2

2.8.2

Beryllium

Magnesium

(c)

2.8

2.8.8

Helium

Neon

Argon

Question: (a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?

(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

Answer: (a) Yes, lithium, sodium and potassium have one electron in their outermost shell. Hence, they have the same valency and belong to Group 1 of the modern periodic table.

(b) The atoms of helium (He) and neon (Ne) have a completely filled outermost shell of electrons. Therefore, they are chemically stable and show very low reactivity.

Very Long Answer Questions and Answers (From 3 Marks to 5 Marks) :

Question: What is Newland’s Law of Octives ? What were the limitations of Newland’s Law of Octaves ? [2020]

Answer: Newlands’ Law of Octaves: When elements are arranged in the increasing order of their atomic masses, every eighth element has properties similar to those of the first element, just like the eighth note in a musical octave.

Limitations of Newlands’ Law of Octaves:

(a) The Law of Octaves was applicable only up to calcium. After calcium, every eighth element did not have properties similar to those of the first element.

(b) Newlands assumed that only 56 elements existed in nature and no more elements would be discovered. However, several new elements were discovered later, whose properties did not fit into the Law of Octaves.

Question: State Modern Periodic Law. How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table ? [2020]

Answer: Modern Periodic Law: Properties of elements are a periodic function of their atomic number.

The anomalies in Mendeleev’s Periodic Table were removed by arranging the elements in the increasing order of their atomic numbers instead of their atomic masses, as atomic number is a fundamental property of an element discovered by Moseley.

Question: What is effective nuclear charge ? How does effective nuclear charge change in group and Period in the Periodic Table ? [2024]

Answer: Effective nuclear charge is the net positive charge experienced by an electron in an atom after considering the shielding effect of other electrons.

Across a period, it generally increases because the nuclear charge increases while shielding remains nearly constant. Down a group, it generally increases slightly or remains nearly constant for valence electrons due to the increase in nuclear charge and shielding effect.

Question: What is the need to classify the elements ? Mention the limitations of Newlands law of octives. [2021]

Answer: The classification of elements is needed to arrange them systematically based on their similar properties. It makes the study of a large number of elements easier and helps us understand and compare their physical and chemical properties, as well as predict the properties of elements.

Limitations of Newlands’ Law of Octaves:

(a) The Law of Octaves was applicable only up to calcium. After calcium, every eighth element did not have properties similar to those of the first element.

Question: (a) Which element has twice as many electrons in its second shell as in its first shell ? [2019]

(b) An atom has electronic configuration 2, 8, 7. What is the atomic number of this element?

(c) Lithium, sodium , potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements ?

Answer: (a) First shell = 2 electron and second shell = 2 × 2 = 4

Therefore, the element is Beryllium (Be) .

(b) Total number of electrons = 2 + 8 + 7 = 17.

Therefore, the atomic number is 17, and the element is Chlorine (Cl) .

(c) Yes, lithium, sodium and potassium have one electron in their outermost shell. Hence, they have the same valency and belong to Group 1 of the modern periodic table.

Question: Which element has ;

(a) two shells , both of which are completely filled with electrons ?

(b) the electronic configuration 2.8.2 ?

(d) a total of two shells, with three electrons in its valence shell ?

(e) twice as many electrons in its second shell as in its first shell ?

Answer: (a) Neon

The electronic configuration of neon is 2.8 .

(b) Magnesium (Mg) .

The electronic configuration of silicon is 2.8.4 .

(d) Boron (B) .

The electronic configuration of neon is 2.3 .

(e) Carbon (C)

The electronic configuration of neon is 2.4 .

Question: An atom has electronic configuration 2.8.7

(a) What is the atomic number of this element ?

(b) To which of the following elements would it be chemically similar ?

[Atomic numbers are given in parentheses.]

N (7) F (9) P (15) Ar (18)

Answer: (a) The atomic number of the element is 17 .

(b)

Name of elements	Atomic numbers	Electronic configuration
N	7	2.5
F	9	2.7
P	15	2.8.5
Ar	18	2.8.8

Nitrogen and phosphorus have the same chemical properties . Because both the element have same number of valency .

Question: Nitrogen (atomic number 7) and Phosphorus (atomic number 15) belong to group 15 of the Periodic Table . Write the electronic configuration of these two elements . Which of these will be more electronegative ? Why ? [SEBA 2018]

Answer:

Atomic numbers	Name of elements	Electronic configuration
7	Nitrogen	2.5
15	Phosphorus	2.8.5

Nitrogen is more electronegative than phosphorus . Because the outermost electrons are nearest from the nucleus .

Question: In the Modern Periodic Table , calcium (atomic number 20) is surrounded by elements with atomic numbers 12 , 19 , 21 and 38 . Which of these have physical and chemical properties resembling calcium ?

Answer:

Atomic numbers	Name of elements	Electronic configuration
20	Ca	2.8.8.2
12	Mg	2.8.2
19	K	2.8.8.1
21	Sc	2.8.8.3
38	Rb	2.8.8.18.2

The elements of atomic number 12 and 38 have the same physical and chemical properties . Because both the element have same number of valency .

Question: The position of three elements A , B and C in the Periodic Table are shown below – [2019]

Group 16	Group 17
------	------
------	A
------	-------
B	C

(a) State whether A is a metal or non-metal .

(b) State whether C is more reactive or less reactive than A

(d) Which type of ion, cation or anion , will be formed by element A ?

Answer: (a) A is a non-metyal .

(b) C is less reactive than A .

(d) Anion .

Posted 2 weeks ago

5. Periodic Classification of elements SEBA/ASSEB Class 10 Science– Important Questions and Answers | Assam HSLC

SEBA/ASSEB Class 10 Science Chapter 5: Periodic Classification of elements Important Questions and Answers | HSLC Assam

Chapter 5: Periodic Classification of elements

Multiple Choice Questions and Answers:

Long Answer Questions and Answers ( From 1 Mark to 2 Marks):

Very Long Answer Questions and Answers (From 3 Marks to 5 Marks) :

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