CBE Questions Chapter 5 Periodic Classification of Elements Science Class 10
Hint: Calculate the average atomic mass given masses of different elements, in order to identify Dobereiner's Triads.
Question.1. The table lists the symbol and atomic mass of three elements.
Which option gives the average atomic mass of the elements that support Dobereiner’s Triads?
(a) (mass of lithium + mass of sodium)/2
(b) (mass of lithium + mass of sodium + mass of potassium)/2
(c) (mass of lithium + mass of potassium)/2
(d) (mass of lithium + mass of potassium – mass of sodium)/2
Question.2. The image shows three set of elements.
Which set of element follows the rule of Dobereiner’s Triads?
(a) W and X
(b) X and Y
(c) Y and Z
(d) Z and X
Ans.1. (c) (mass of lithium + mass of potassium)/2
Ans.2. (d) Z and X
Hint: Arrange elements in order of increasing atomic masses, in order to form Newlands' Octaves.
Question.3. Newland arranged some elements in order of increasing atomic masses and formed Newlands’ Octaves. Which option arranges the elements in order to form Newlands’ Octaves?
(a) 
(b) 
(c) 
(d) 
Question.4. How Chlorine, Bromine, Fluorine, Cobalt, and Hydrogen be arranged in order to satisfy the concept of Newlands’ Octaves?
(a) Chlorine, Bromine, Fluorine, Cobalt, Hydrogen
(b) Hydrogen, Fluorine, Bromine, Cobalt, Bromine
(c) Fluorine, Chlorine, Cobalt, Bromine, Hydrogen
(d) Cobalt, Bromine, Hydrogen, Fluorine, Chlorine
Ans.3. (c)
Ans.4. (b) Hydrogen, Fluorine, Bromine, Cobalt, Bromine
Hint: Arrange the elements on the basis of their properties like oxides and hydrides, in order to form Mendeleev's Periodic Table.
Question.5. The image shows the arrangement of the elements in the Mendeleev’s Periodic Table done by a student.
What is the error done by the student while arranging the elements?
(a) The student arranged hydrogen in the first group.
(b) The student arranged chlorine and fluorine in the seventh period.
(c) The student arranged the elements of the third period in the fourth period.
(d) The student arranged the elements of the third group in the second group.
Question.6. Which option arranges the elements of period four in the correct groups?
(a) 
(b) 
(c) 
(d) 
Ans.5. (d) The student arranged the elements of the third group in the second group.
Ans.6. (c)
Hint: Identify the achievements and limitations in Mendeleev’s periodic table with respect to arrangement of elements.
Question.7. Which option describes the achievements of the Mendeleev’s Periodic Table?
(a) prediction of noble gases
(b) it eliminated the blank spaces left in the table
(c) predicting that the elements can be arranged based on their properties
(d) an element in a trend has an average atomic mass of the elements above and below it
Question.8. A student studies about Mendeleev’s periodic table and lists some statements.
P: No fixed position was given to carbon in the periodic table.
Q: The atomic masses do not increase in a regular manner.
R: Isotopes of an element have different chemical properties but similar masses.
Which option lists the limitations of the Mendeleev’s Periodic Table?
(a) only P
(b) only R
(c) both P and Q
(d) both Q and R
Ans.7. (a) prediction of noble gases
Ans.8. (a) only P
Hint: Interpret the arrangement of elements in the MPT.
Question.9. Which option arranges the elements based on increasing atomic numbers based on the Modern Periodic Table?
(a) C\rightarrow N \rightarrow O \rightarrow Ne \rightarrow F
(b) S\rightarrow Ar \rightarrow Cl \rightarrow Ca \rightarrow K
(c) H\rightarrow Li \rightarrow He \rightarrow Be \rightarrow B
(d) Na\rightarrow Mg \rightarrow Al \rightarrow Si \rightarrow P
Question.10. A student studying Modern periodic table arranges some elements in different groups, as shown.
Which group supports the guidelines of the Modern Periodic table?
(a) group 1
(b) group 18
(c) groups 1 and 2
(d) groups 1 and 18
Ans.9. (d) Na\rightarrow Mg \rightarrow Al \rightarrow Si \rightarrow P
Ans.10. (d) groups 1 and 18
Hint: Compute the group and period number of an element given its atomic number, in order to determine its place in MPT.
Question.11. The image shows an element with its atomic number and mass number. 
Which option arranges the element in the periodic table?
(a) group: 1; period: 1
(b) group: 5; period: 3
(c) group: 10; period: 1
(d) group: 15; period: 3
Question.12. An element X has atomic number 9. In which period and group, it can be placed in the modern periodic table?
(a) 
(b) 
(c) 
(d) 
Ans.11. (d) group: 15; period: 3
Ans.12. (a)
Hint: Compute the number of shells & valence electrons of an element given its position in MPT, in order to determine its properties.
Question.13. Boron is a non-metal and is placed under group 13 and period 2. How can boron form bonds with other elements?
(a) by sharing 5 electrons
(b) by sharing 3 electrons
(c) by sharing 2 electrons
(d) by sharing 1 electron
Question.14. An element has atomic number 20 and in group 2 and period 4. Which option gives the number of valence electrons and shells present in the element?
(a) 
(b) 
(c) 
(d) 
Ans.13. (b) by sharing 3 electrons
Ans.14. (b)
Hint: Predict the position of elements in the MPT in order to explain the trends in groups and periods.
Question.15. What is the trend of valency along the periods in the modern periodic table?
(a) it increases from left to right
(b) it decreases from right to left
(c) it increases and then decreases
(d) it decreases and then increases
Question.16. The image shows the list of elements in group 2. 
What will be the trend of valency as one goes from Beryllium to Radium?
(a) it will remain the same
(b) it will increase till radium
(c) it will decrease and then increase after calcium
(d) it will increase and then decrease after calcium
Ans.15. (c) it increases and then decreases
Ans.16. (a) it will remain the same
Hint: Predict the trend of atomic size across the period and down the group, in order to explain arrangement of elements in MPT.
Question.17. A student learns that the atomic size depends on the atomic radius of the elements. How does the atomic radius of elements in the third-period change as one goes from sodium to argon?
(a) atomic radius increases from sodium to argon
(b) atomic radius decreases from sodium to argon
(c) atomic radius increases as new shells are added
(d) atomic radius decreases due to the addition of new shells
Question.18. A student notices that the atomic mass of elements of group 1 increases as one moves from hydrogen to cesium, as shown. 
Which option gives the reason for the increasing atomic mass?
(a) addition of shells
(b) an increase in nuclear charge
(c) addition of electrons in the same shells
(d) decrease indistance between the outermost electrons and nucleus
Ans.17. (b) atomic radius decreases from sodium to argon
Ans.18. (a) addition of shells
Hint: Analyse the usefulness of MPT in studying the chemical behaviour of elements.
Question.19. What is the order of the metallic character down the group?
(a) it decreases as new shells are added to the element
(b) it increases as electrons move away from the nucleus
(c) increases as new atoms are added in the same shell
(d) it decreases as the effective nuclear charge on the electron increases
Question.20. Electronegativity is defined as the ability of an element to form bonds by gaining electrons. How does the electronegativity of elements vary across the periods?
(a) it increases as the number of shells increases
(b) decreases as the number of shells decreases
(c) increases as the more of electrons are added to the same shell
(d) it decreases as the more of electrons are added to the same shell
Ans.19. (b) it increases as electrons move away from the nucleus
Ans.20. (c) increases as the more of electrons are added to the same shell