# NCERT Exemplar Problems and their Solutions

##### Grade X - Chemistry

Reviewed By:
Krishna Kant Majee
M.Sc., B.Ed.

### Chapter 5-Periodic Classification of Elements-MCQs

Q.1. Upto which element, the law of octaves was found to be applicable?
(a) Oxygen
(b) Calcium
(c) Cobalt
(d) Potassium
Answer. (b)
Explanation: Newlands’ law of octaves could be applicable for elements having low atomic masses upto 40 u.
Q.2. 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
(c) Increasing atomic masses
(d) Decreasing atomic masses
Answer (c)
Explanation: The Mendeleev’s periodic law is an arrangement of elements in increasing order of their atomic masses as Mendeleev’s periodic law states that, the physical and chemical properties of elements are a periodic function of their atomic masses.
Q.3 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 periodic table later?
(a) Germanium
(b) Chlorine
(c) Oxygen
(d) Silicon
Answer. (a)
Explanation: Germanium element found a place in the periodic table later in the place of Eka–silicon in Mendeleev’s periodic table.

Q.4. Which of the following statement(s) about the modern periodic table are incorrect?
(i) The elements in the modern periodic table are arranged on the basis of their decreasing atomic numbers.
(ii) The elements in the modern periodic table are arranged on the basis of their increasing atomic masses.
(iii) Isotopes are placed in adjoining group(s) in the periodic table.
(iv) The elements in the modern periodic table are arranged on the basis of their increasing atomic number.
(a) Only (i)
(b) (i), (ii) and (iii)
(c) (i), (ii) and (iv)
(d) Only (iv)
Answer. (b)
Explanation: The modern periodic table is tabular arrangement of elements in increasing order of their atomic number therefore isotopes are paced at same position.
Q.5. 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 rows known as periods.
(c) It has 18 vertical columns known as groups.
(d) It has 7 horizontal rows known as groups.
Answer. (c)
Explanation: There are 18 vertical columns, known as groups and 7 horizontal rows in Modern periodic table.
Q.6. 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)
Explanation: Second period of Modern Periodic table contains elements from atomic number 3 to 10.
Q.7. The elements A, B, C, D and E have atomic number 9, 11, 17, 12 and 13 respectively. Which pair of elements belongs to the same group?
(a) A and B
(b) B and D
(c) A and C
(d) D and E
Answer. (c)
Explanation: Elements having the same number of valence electrons belong to the same group.
Given elements and their electronic configurations are written below:

 Element Electronicconfiguration A (9) 2, 7 B (11) 2, 8, 1 C (17) 2, 8, 7 D (12) 2, 8, 2 E (13) 2, 8, 3

As, both A and C elements have the same number of valence electrons which is 7, hence they belong to the same group, i.e. 17th group of periodic table.
Q.8. Where would you locate the element with electronic configuration 2, 8 in the modern periodic table?
(a) Group 8
(b) Group 2
(c) Group 18
(d) Group 10
Answer. (c)
Explanation: Element with electronic configuration 2, 8 has octet configuration so must be an inter gas which is placed in group 18.
Q.9. An element which is an essential constituent of all organic compounds belongs to
(a) Group 1
(b) Group 14
(c) Group 15
(d) Group 16
Answer. (b)
Explanation: Carbon is an essential element for all organic compounds and belongs to group 14.
Q. 10. 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)
Explanation: The elements of 2nd period contain two shells; K and d L shell.
Q.11. Which one of the following elements exhibit maximum number of valence electrons?
(a) Na
(b) Al
(c) Si
(d) P
Answer. (d)
Explanation: As the group number increases, number of valence electrons also increases.
Q.12. Which of the following gives the correct increasing order of the atomic radii of O, F and N?
(a) O, F, N
(b) N, F, O
(c) O, N, F
(d) F, O, N
Answer. (d)
Explanation: From left to right in the Modern Periodic table, the atomic radii decrease with increasing the atomic number. The atomic number of F, O and N are 9, 8 and 7 respectively so atomic radius will decrease from N to F.
Q.13. Which among the following elements has the largest atomic radii?
(a) Na
(b) Mg
(c) K
(d) Ca
Answer. (c)
Explanation: Na and Mg belong to same period whereas Na and K are in the same group. I a group from top to bottom, atomic radius increase whereas it decreases in period from left to right. Hence the order would be K> Na >Mg and K> Ca> Mg.
Q.14. Which of the following elements would lose an electron easily?
(a) Mg
(b) Na
(c) K
(d) Ca
Answer. (c)
Explanation: Na and K are alkali metals whereas Mg and Ca are alkaline earth metals. Alkali metals are morel electropositive compare to alkaline earth metals and can easily lose electrons. Out of Na and K, K will easily lose electrons because of bigger size and less electronic attraction.
Q.15. Which of the following elements does not lose an electron easily?
(a) Na
(b) F
(c) Mg
(d) Al
Answer. (b)
Explanation: Metals can easily lose electrons and exhibit electropositive nature whereas non-metals have tendency to accept electrons and exhibit electronegative nature. Na, Al and Mg are metals whereas F is a non-metal.
Q.16. Which of the following are the characteristics of isotopes of an element?
(i) Isotopes of an element have same atomic masses.
(ii) Isotopes of an element have same atomic number.
(iii) Isotopes of an element show same physical properties.
(iv) Isotopes of an element show same chemical properties.
(a) (i), (iii) and (iv)
(b) (ii), (iii) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)
Answer. (d)
Explanation: Isotopes are the atoms of the same element which have same atomic number but different number of neutrons hence their atomic masses are different.
Q.17. 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
(c) Na > Al > Mg > Cl > Si
(d) Al > Na > Si > Ca > Mg
Answer. (b)
Explanation: As we move from left to right in periodic table, metallic characters decreases and non-metallic characters increases. Here Na, Si, Cl, Mg, Al belong to same period so we have to check their position in period.
Q.18. 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
(c) F < O < C < Be < Li
(d) F < O < Be < C < Li
Answer. (b)
Explanation: These all elements belong to same period in which non-metallic characters increases from left to right.
Q.19. What type of oxide would Eka-aluminium form?
(a) $EO_{3}$
(b) $E_{3}O_{2}$
(c) $E_{2}O_{3}$
(d) EO
Answer. (c)
Explanation: Eka-aluminium was later identified as Gallium with valency of 3. Hence the oxide would be$E_{2}O_{3}$.
Q.20. Three elements B, Si and Ge are
(a) Metals
(b) Non-metals
(c) Metalloids
(d) Metal, non-metal and metalloid respectively
Answer. (c)
Explanation: The elements boron (B), silicon (Si) and germanium (Ge) exhibit intermediate properties of metals and non-metals therefore they are called as metalloids. These elements are placed in between metals and non-metals as zigzag line to separate them.
Q.21. Which of the following elements will form an acidic oxide?
(a) An element with atomic number 7
(b) An element with atomic number 3
(c) An element with atomic number 12
(d) An element with atomic number 19
Answer. (a)
Explanation: Formation of acidic oxides is character of non-metals. Here element with atomic number 7 is a non-metal that is nitrogen. Rests of all are metals.
Q.22. The element with atomic number 14 is hard and forms acidic oxide and a covalent halide. To which of the following categories does the element belong?
(a) Metal
(b) Metalloid
(c) Non-metal
(d) Left-hand side element
Answer. (b)
Explanation: Atomic number 14 is for Silicon element which is a metalloid and exhibit properties of both metals and non-metals. It has 4 electrons in its valence shell so tends to form covalent acidic oxide like non-metals.
Q.23. Which one of the following depict the correct representation of atomic radius (r) of an atom?

(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
Answer. (b)
Explanation: The distance between the centre of the nucleus and the outermost shell is known as atomic radius.
Q.24. Which one of the following does not increase while moving down to group of the periodic table?
(a) Atomic radius
(b) Metallic character
(c) Valence
(d) Number of shells in an element
Answer. (c)
Explanation: Elements of the same group have same number of valence electrons hence valency will remain same.
Q.25. On moving from left to right in a period in the periodic table, the size of the atom
(a) increases
(b) decreases
(c) does not change appreciably
(d) first decreases and then increases
Answer. (b)
Explanation: As we move from left to right in the period of periodic table, the number of shell remains same but atomic number increases. So the electronic attraction over valence electrons also increases that decreases the atomic radius.
Q.26. Which of the following set of elements is written in order of their increasing metallic character?
(a) Be, Mg, Ca
(b) Na, Li, K
(c) Mg, Al, Si
(d) C, O, N
Answer. (a)
Explanation: As we move down in a group, metallic nature increases. Be, Mg and Ca belong to same group that is group 2 of Modern Periodic table.