Extra Questions of Class 10 Science Chapter 5 Periodic Classification of Elements PDF Download

We have provided you with Extra and Important Questions from Class 10 Science Chapter 5 Periodic Classification of Elements. This Extra and Important Questions will help you to score 100% in your Board Exams. These extra questions will be helpful to revise the important topics and concepts.

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Periodic Classification of Elements Class 10 Important Questions with Answers Science Chapter 5

Extra Questions for Class 10 Science Chapter 5 Very Short Answer Type

Question: Name two elements whose properties were predicted on the basis of their positions in Mendeleev’s periodic table.

Answer: Gallium (Eka-aluminium) and germanium (Eka-silicon).

Question: Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev. [NCERT Exemplar]

Answer: Eka-aluminium represents gallium (Ga) with valency three and Eka-silicon is for germanium (Ge) with valency four. The formulae of their respective chlorides are GaCl3 and GeCl4

Question: How many elements are there in period 2?

Answer: Eight (8)

Question: Name all the elements present in group-17 of the Modern Periodic Table.

Answer: F, Cl, Br, I, At.

Question: Name two elements whose atomic weight were corrected on the basis of their position in Mendeleev’s periodic table.

Answer: Gold (Au) and platinum (Pt).

Question: Arrange the following elements in the increasing order of their metallic character.
Mg, Ca, K, Ge, Ga     [NCERT Exemplar]

Answer:Ge < Ga Mg < Ca < K.

Question:Name the scientist who proposed the Modern Periodic Law.

Answer:Henry Moseley, a scientist, proposed the Modern Periodic Law.

Question:What is meant by a group in the periodic table?

Answer:Groups are the vertical columns/vertical lines in the periodic table.

Question:What is meant by a period in the periodic table?

Answer:Periods are the horizontal rows in the periodic table.

Question:Name the elements present in period 1 of the modern periodic table.

Answer:Hydrogen (H) and Helium (He).

Question:An element A is in group II (group 2) of the periodic table:
(а) What will be the formula of its chloride?
(b) What will be the formula of its oxide?

Answer:(a) ACl2
(b) AO.

Question:Why are the elements calcium, strontium and barium named as alkaline earths?

Answer:These elements are called alkaline earths because their oxides are alkaline in nature and exist in the earth.

Question:Give the name and electronic configuration of second alkali metal.

Answer:The second alkali metal is sodium (Na). Its electronic configuration is 2, 8, 1.

Question:What are Metalloids?

Answer:Those elements which show some properties of both metals and non-metals are called metalloids. Examples: Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium and Polonium.

Question:Name three elements whose atomic masses were correct on the basis of their positions in Mendeleev’s periodic table.


  1. Beryllium (Be, group II A)
  2. gold (Au, group II B)
  3. platinum (Pt, group VIII).

Question:Name the inert gas which has two electrons in its valence shell.


Question:Name the most metallic and most non-metallic element in the Periodic Table.

Answer:The most metallic elements is francium (group 1) and most non-metallic element is fluorine (group 17).

Question:In the Modern Periodic Table, which are the metals among the first ten elements?


Lithium (Li), Beryllium (Be) and Boron (B) are the metal elements among first ten elements in the Modern Periodic Table.

Question:Two elements A and B belong to the same period. What is common in them?


They have the same number of shells.

Question:Calcium, Strontium and Barium form a Dobereiner’s triad. The atomic masses of calcium and Barium are 40 and 137 respectively. Predict the atomic mass of strontium.

Answer:According to Dobereiner’s triad, atomic mass of strontium is the arithmetic means of Ca and Ba as strontium lies between Ca and Ba.

Atomic mass of Sr = 40+137/ 2=177/ 2=88.5

Extra Questions for Class 10 Science Chapter 5 Short Answer Type

Question:The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called? Give one example of such a set of elements.   [NCERT Exemplar]


The arrangement of these elements is known as Dobereiner triad. Example, Lithium, sodium and Potassium.

Question:In group I of the periodic table, three elements X, Y and Z have atomic radii 1.33 A, 0.95 A and 0.60 A respectively. Arrange the elements (X, Y and Z) in the increasing order of atomic number and mention a suitable reason for it.


In a given group, the atomic radii increases on moving down the group. Therefore, the arrangement of the given elements in the increasing order of their atomic numbers is as follows: Z, Y, X.

Question:Elements have been arranged in the following sequence on the basis of their increasing atomic masses.
F, Na, Mg, Al, Si, P, S, Cl, Ar, K
(a) Pick two sets of elements which have similar properties.
(b) The given sequence represents which law of classification of elements?   [NCERT Exemplar]


(a) F and Cl are first and eighth element in the above sequence, therefore, they have similar properties.
Please note that although Na and K have similar properties but they are not related as first and eighth element in the above sequence.

(b) This sequence represents Newland’s Law of Octaves.

Question:State and explain Mendeleev’s periodic law.


According to Mendeleev’s periodic law “Physical and chemical properties of elements are periodic function of their atomic masses”.

Question:“Hydrogen occupies a unique position in the Modern Periodic Table”. Justify the statement.   [NCERT Exemplar]


The position of the element hydrogen is still not clear even in the Modern Periodic Table.

In electronic configuration, it resembles alkali metals of group 1. All of them have only one electron in the valence shell. Actually, hydrogen has only one shell (K-shell) which has one electron.

In characteristics, it resembles halogens of group 17. For example, like halogens hydrogen is a non-metal and diatomic as well. It has been therefore, decided to assign hydrogen a unique position in the Modern or Long Form Periodic Table. It is placed at the top in group 1 of alkali metals. However, it is not a member of that group.

Question:If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride?  [NCERT Exemplar]


Since element “X’ is placed in group 14, therefore, its valency is 14 – 10 = 4. Further, since it is difficult to either lose all the four valence electrons or gain four more electrons, therefore, it prefers to share these four electrons to acquire the stable electronic configuration of the nearest inert gas. Its formula will be XCl4. Thus, the nature of the chloride of element ‘X’ is covalent.

Question:Explain clearly, why atomic number of an element is most important to the chemist than its relative atomic mass.


Atomic number corresponds to the number of electron in an atom or it reflects the electronic configuration of the element. The elements having similar electronic configurations can then be placed together in the same group, it helps in the systematic classification of elements.

On the other hand, the atomic mass of an element does not provide the electronic configuration of an element, so atomic number is more fundamental property for classification of elements.

Question:How many groups and periods are there in the modern periodic table? How do the atomic size and metallic character of elements vary as we move: (a) down a group and (b) from left to right in a period. [Delhi 2015]


Number of groups is 18 and number of periods in the modern periodic table is 7.
(a) All the elements in a group have the same valency. On going down in a group, the atomic size increases because a new shell of electrons is added to the atoms at every step.

(b) On moving from left to right in the periodic table, the valency of the elements first increases from 1 to 4 and then decreases to zero. On moving from left to right in a period, the metallic character of elements decrease because on moving from left to right in a period, the electropositive character of elements decrease.

Question:Identify the elements with the following property and arrange them in increasing order of their reactivity.
(a) An element which is a soft and reactive metal.
(b) The metal which is an important constituent of limestone.
(c) The metal which exists in liquid state at room temperature.  [NCERT Exemplar]

Answer:(a) Alkali metals are soft and reactive. For example, Na, K, etc.
(b) Limestone is calcium carbonate, therefore, the important constituent of limestone is calcium.
(c) Metals which exists in the liquid state at room temperature are Mercury (Hg).

Question:(a) State modern periodic law.
(b) What are the advantages of the long form of the periodic table over Mendeleev’s periodic table?


(a) According to modern periodic law “physical and chemical properties of elements are periodic function of their atomic numbers”.

(b) (i) Classification of elements on the basis of atomic number is more closer to chemical properties.
(ii) No separate places for isotopes of an element are required.
(iii) In case of Ar and K, Ar has less atomic number so it should be placed before K according to the increasing order of atomic number.

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.
(c) Three elements with filled outermost shells.

Answer:(a) Lithium (Li), Sodium (Na), Potassium (K)
(b) Magnesium (Mg), Calcium (Ca)
(c) Helium (He), Neon (Ne), Argon (Ar)

Question:Two elements X and Y belong to group 1 and 2 respectively in the same period of periodic table. Compare them with respect to:   [CBSE 2011]
(i) the number of valence electrons in their atoms
(ii) their valencies
(iii) metallic character
(iv) the sizes of their atoms
(v) the formulae of their oxides
(vi) the formulae of their chlorides.


X and Y belong to same period.

  • X belongs to group ‘1’.
  • Y belongs to group ‘2’.

(i) Valence electron in X is 1 whereas valence electrons in Y are 2.
(ii) The valency of X is 1 whereas valency of Y is 2.
(iii) X is more metallic than Y because metallic character decreases on moving from left to right in a period.
(iv) The size of X is more than Y because size of the atom decreases on moving from left to right in a period.
(v) Oxide of X = X2O,   Oxide of Y = YO
(vi) Chloride of X = XCl,   Chloride of Y = YCl2

Question:The element Li, Na and K, each having one valence electron, are in period 2, 3 and 4 respectively of the Modem Periodic Table.
(a) In which group of the periodic table should they be?
(b) Which one of them is least reactive?
(c) Which one of them has the largest atomic radius? Give reason to justify your answer in each case. [CBSE 2013]

Answer:(a) Since the elements have one valence electron, they are placed in group 1 (Alkali metals) in the order Li (period = 2); Na (period = 3); K (period = 4).

(b) Since the reactivity of the elements increases down a group, the element Li is the least reactive chemically.

(c) Since the atomic size increases down a group, the element K has the large atomic size or atomic radius out of these elements.

Question:Explain why are the following statements not correct:
(a) All groups contain metals and non-metals.
(b) Atoms of elements in the same group have the same number of electron(s).
(c) Non-metallic character decreases across a period with increase in atomic number.
(d) Reactivity increases with atomic number in a group as well as in a period.   [2010]

Answer:(a) Because all groups do not contain metals and non-metals. For example, Alkali metal group contains metals only.
(b) Atom of the elements in the same group have same number of electrons in the valence shell.
(c) Non-metallic character increases across a period with increase in atomic number.
(d) Reactivity increases with atomic number in a group but not across a period.

Question:Atomic number of an element is 16. Predict
(i) the number of valence electrons in its atom
(ii) its valency
(iii) its group number
(iv) whether it is a metal or a non-metal
(v) the nature of oxide formed by it.
(vi) the formula of the chloride   [CBSE2011]

Answer:The element with atomic number Z = 16 is sulphur. The electronic configuration of the element is 2, 8, 6.
(i) The number of valence electrons is 6
(ii) The valency of the element is 2 (8 – 6 = 2)
(iii) The group number of the element is 16.
(iv) The element is a non-metal.
(v) Since the element is non-metal, its oxide is acidic in nature. Actually, two oxides are formed. These are SO2 and SO3. Both are of acidic nature.
(vi) The formula of the chloride is SCl2.

Extra Questions for Class 10 Science Chapter 5 Long Answer Type

Question:(a) Why do we classify elements?
(b) What were the two criteria used by Mendeleev in creating his Periodic Table?
(c) Why did Mendeleev leave some gaps in his Periodic Table?
(d) In Mendeleev’s Periodic Table, why was there no mention of Noble gases like Helium, Neon and Argon?
(e) Would you place the two isotopes of chlorine, Cl-35 and Cl-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.


(a) As different elements were being discovered, scientists gathered more information about the properties of these elements. It was observed that it was difficult to organise all the information or properties of these elements. So scientists started discovering some pattern in their properties to classify all the known elements to make their study easier.

(b) Atomic mass and similarity of chemical properties (compounds formed by elements with oxygen and hydrogen) were the two criteria used by Mendeleev in his Periodic Table.

(c) Mendeleev left some gaps in his Periodic Table as he predicted the existence of some elements that had not been discovered at that time.

(d) Noble gases like helium, neon, argon, etc. were not mentioned in Mendeleev’s Periodic Table because these gases were discovered later as they are very inert and present in extremely low concentrations in our atmosphere. After the discovery of noble gases they could be placed in a new group without disturbing the existing order of the Periodic Table.

(e) The Modem Periodic Table states that properties of elements are a periodic function of their atomic numbers, since Cl-35 and Cl-37 isotopes have the same atomic number (17), hence they will have same chemical properties even though their atomic masses are different. So, they should be placed in the same slot of the periodic table.

Question:Atomic number of a few elements are give below:
10, 20, 7, 14
(a) Identify the elements.
(b) Identify the Group number of these elements in the Periodic Table.
(c) Identify the Periods of these elements in the Periodic Table.
(d) What would be the electronic configuration for each of these elements?
(e) Determine the valency of these elements.  [NCERT Exemplar]

Answer:(a) The element are: Neon (Z = 10), Calcium (Z = 20), Nitrogen (Z = 7) and Silicon (Z = 14).
(b) Group number: Neon (18), Calcium (2), Nitrogen (15), Silicon (14).
(c) Periods: Neon (2), Calcium (4), Fluorine (2), Silicon (3).
(d) Electronic Configuration: Neon (2, 8); Calcium (2, 8, 8, 2); Nitrogen (2, 5); Silicon (2, 8, 4).
(e) Valency: Neon (zero); Calcium (2); Nitrogen (3); Silicon (4).

Question:The elements of one short period of the periodic table are given below in the order from left to right.
Li, Be, B, C, O, F, Ne,
(a) To which period these elements belong?
(b) One element of this period is missing. Which is the missing element and where should it be placed?
(c) Which one of the element in this period shows the property of catenation?
(d) Place the three elements fluorine, beryllium and nitrogen in the order of increasing electronegativity.
(e) Which one of the above elements belong to the halogen series?

Answer:(a) Second period (Atomic number: 3-10)
(b) Nitrogen (N), It should be placed between Carbon (Atomic number 6) and Oxygen (Atomic number 8)
(c) Carbon
(d) Be, N, F
(e) Fluorine.

Question:Which element has
(a) two shells, both of which are completely filled with electrons?
(b) the electronic configuration 2, 8, 2?
(c) a total of three shells, with four electrons in its valence shell?
(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 [Ne] (2, 8)
(b) Magnesium [Mg]
(c) Silicon [Si] (2, 8, 4)
(d) Boron [B] (2, 3)
(e) Carbon [C] (2, 4).

Question:The electronic configuration of an element T is 2, 8, 7.
(а) What is the group number of T?
(b) What is the period number of T?
(c) How many valence electrons are there in an atom of T?
(d) Is it a metal or non-metal?

Answer:(a) Group-17
(b) Third period
(c) 7
(d) Non-metal.

Question:Mendeleev predicted the existence of certain elements not known at that time and named two of them as Eka-silicon and Eka-aluminium.
(a) Name the elements which have taken the place of these elements.
(b) Mention the group and the period of these elements in the Modern Periodic Table.
(c) Classify these elements as metals, non-metals or metalloids.
(d) How many valence electrons are present in each one of them?  [NCERT Exemplar]

Answer:(a) Eka-silicon for germanium (Ge) and Eka-aluminium for Gallium (Ga).
(b) Group number of Ga is 13 and its period is 4th and group number of Ge is 14 and its period is also 4th.
(c) Both Ga and Ge are metalloids.
(d) Ga lies in group 13, therefore, it has 13 – 10 = 3 valence electrons. Similarly, Ge lies in group 14 and hence it has 14 – 10 = 4 valence electron.

Question:(a) Electropositive nature of the element(s) increases down the group and decreases across the period.
(b) Electronegativity of the element decreases down the group and increases across the period.
(c) Atomic size increases down the group and decreases across a period (left to right).
(d) Metallic character increases down the group and decreases across a period.
On the basis of the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9.
(a) Name the most electropositive element among them
(b) Name the most electronegative element
(c) Name the element with smallest atomic size
(d) Name the element which is a metalloid
(e) Name the element which shows maximum valency.  [NCERT Exemplar]

Answer:(a) Lithium (Z = 3) is the most electropositive element.
(b) Fluorine (Z = 9) is the most electronegative element.
(c) Fluorine (Z = 9) has the smallest atomic size.
(d) Boron (Z = 5) is a metalloid.
(e) Carbon (Z = 6) shows the maximum valency (4).
However, the element nitrogen (Z = 7) can show valency 5 in some compounds (example, N2O5).

Question:First systematic classification was done by Mendeleev. He arranged the elements in the increasing order of atomic masses. Elements with similar properties lies in a group, he left certain gaps for unknown elements.
(i) Name two elements for which blank spaces were left out by Mendeleev.
(ii) List two main drawbacks of the Mendeleev’s periodic classification.
(iii) Mention the values exhibited by Mendeleev.

Answer:(i) Gallium (Ga), Germanium (Ge).
(ii) (a) Position of hydrogen.
(b) Position of isotopes.
(iii) Use of knowledge of Chemistry, Thinking ability

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