# CBSE Important Questions(Short questions) for CBSE Class 10 Science PERIODIC CLASSIFICATION OF ELEMENTS

QUESTIONS:- (1 mark each)
Q1. What is meant by classification of elements?
Q2. What was the limitation of Dobereiner law of triads?
Q3. Why do Li, Na and K how resemblance on the basis of Dobereiner’s law of triads?
Q4. Classify the following elements according to the Law of Octaves:
K, Na, Ca, S, O, P, Al
N, F, Si, C, Cl, Mg
Q5. A, B and C are elements of Dobereiner’s triad. If the atomic mass of A is 7 and that of C s 23, what will be the atomic mass of B.
Q6. Classify the following elements into groups of triads
Cl,  Ca,  Ba,  Sr,  K,  Li,  Br,  I,  Na
Q7. Na and K resemble in their properties, how many elements are there between them?
Q8. State Mendeleev’s law.
Q9. Mendeleev classified the elements on the basis of two factors. What were these two factors?
Q10. What is meant by ‘groups’ of Periodic Table?
Q11. What is meant by periodicity of properties?
Q12. Name two elements whose valencies are equal to their group number.
Q13. What are the elements of group 1 and group 17?
Q14. Which one has the bigger size?
Na (11) or Cl (17), Cl (17) or F (9)
Q15. What would be the nature of oxides formed by the element on the left hand side of the periodic table? Give one example.
Q16. How many shells are present in the elements of 3rd period? Give reason also.
Q17. An element ‘X’ has atomic number 20. To which group and period does it belong?
Q18. Find the atomic number of the element whose electronic configuration is 2, 8, 5.
Q19. Arrange the following elements increasing order of their atomic radii:
Li, Be, F, N
Cl, At, Br, I
Q20. Out of Li and K, which will have stronger metallic character and why?
Q21. Write the number of horizontal rows in the modern periodic table. What are these rows called?
Q22. Give the number of elements in 2nd and 5th period in Modern Periodic Table.

QUESTIONS: (2 marks each)
Q1. The elements of the third period of the Periodic Table are given below:
Group →    I       II       III      IV        V        VI       Vii
Period
↓
3         Na     Mg      Al     Si          P         S         Cl
(a) Which is more non – metallic, S or Cl?
(b) Which has higher atomic mass, Al or Cl?
Q2. Give the symbol for
a metal of group 2
a metal of group 13
two non- metals of group 16
most reactive non- metal of group 17.
Q3. Why does atomic size progressively become smaller (atomic radius decreases from Na to Cl)?
Q4. Calcium is an element with atomic number 20.
Is it a metal or a non – metal?
Is it more reactive than Mg or less reactive?
What will be its valency?
What would be the formula of its chloride?
Will it be larger than K or smaller?
Q5. This questions refer to the elements of periodic table with atomic numbers 3 to 18.
Which of them are noble gases?
Which of them are halogens?
Which of them are alkali metals?
Which are the elements with valency 4?
Q8. An element with atomic number 3 combines with another element with atomic number 17. What would be the formula of the compound?
Q9. What is the electronic configuration of the element with atomic number 10?
Q10. What is meant by periodic? What are its causes?
Q11. (i) Mention one property each of elements in a group and of element in a period in Modern Periodic Table.
(ii) What is the number of valence electrons in magnesium and sulphur whose atomic numbers are 12 and 16 respectively?
Q12. Elements A, B, C and D have atomic numbers 1, 8, 11 and 19 respectively. Choose the odd element and give reason for your answer.
Q13. Out of Li and K, which will have stronger metallic character and why?
Q14. Fluorine (9) is more reactive than chlorine (17). Write the reason.
Q15. The atomic radii of three elements A, B and C of the Periodic Table are 186 pm, 104 pm and 1433pm respectively. Giving a reason, arrange these elements in the increasing order of atomic numbers in the period.
Q16. An atom has electronic configuration 2, 8, 7.
What is the atomic number of this element?
To which of the following elements would it be chemically similar?
N (7),     F (9),     P (15),     Ar (18)
Q17. Calcium s an element with atomic number 20.
Will it be a metal/ non- metal?
What will be its valency?
What would be the formula of its chloride?
Will it be larger/ smaller than K? Give a reason for your answer.
Q18. How does the tendency to gain electrons changes from Group 1 to Group 17? Give reason for your answer.
Q19. The atomic number of elements A, B, C, D and E are given below:
Element A B C D E
Atomic no. 7 10 12 4 19
From the above table, answer the following questions:
Which two elements are chemically similar?
Which is an inert gas?
Which element belongs to 3rd period of Periodic Table?
Which element among these is a non – metal?
Q20. The atomic number of S and Cl is 16 and 17 respectively and they belong to the same period .
which one would have smaller atomic size ?
which one would be more electronegative ?
to which group would each one belong ?
Q21. Name three elements which have seven electrons in their outermost shell. How do their non metallic character and atomic size change down the group?
Q22. Locate the position in Periodic Table of the following elements on the basis of their properties:
An element which is an inert gas with atomic number 10.
An element which is tetravalent and basic element of organic chemistry.
A soft metal stored under kerosene and cut with knife.
Q23. Two elements X and Y have atomic number 12 and 16 respectively.
Write the electronic configuration off both.
Which type of bond will they form?
Write the formula of the compound formed by their combination (in term of X and Y).
Q24. Why do all the elements of the
same group have similar properties,  same period have different properties?
Q25. How does the electronic configuration of n atom of an element relate to its position in the Modern Periodic Table? Explain with one example.

Given below are the links of some of the reference books for class 10 Science.

You can use above books for extra knowledge and practicing different questions.

### Practice Question

Question 1 Which among the following is not a base?
A) NaOH
B) $NH_4OH$
C) $C_2H_5OH$
D) KOH
Question 2 What is the minimum resistance which can be made using five resistors each of 1/2 Ohm?
A) 1/10 Ohm
B) 1/25 ohm
C) 10 ohm
D) 2 ohm
Question 3 Which of the following statement is incorrect? ?
A) For every hormone there is a gene
B) For production of every enzyme there is a gene
C) For every molecule of fat there is a gene
D) For every protein there is a gene

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