Which of the following statements is not a correct statement about the trends wlien going from left to right across the periods of Periodic Table. (a) The elements become less metallic in nature. (b) The number of valence electrons increases. (c) The atoms lose their electrons more easily. (d) The oxides become more acidic. Answer: (c) The atoms lose their .electrons more easily.
Element X forms a chloride with the formula XCl2, which is solid with a high melting point. X would most likely to be in the same group of the periodic table as (a) Na (b) Mg (c) Al (d) Si Answer: (b) Mg
Which of the following is the outermost shell for elements of 2nd period? [NCERT Exemplar] (a) K-shell (b) L-shell (c) M-shell (d) N-shell Answer: (b) The elements of 2nd period involve the filling of 2nd shell, i.e. Z-shell. Because in period 2, there are two shell, K and L
An element which is an essential constituent of all organic compounds belongs to [NCERT Exemplar] (a) group 1 (b) group 14 (c) group 15 (d) group 14 and Hydrogen Answer: (d) Constituent of all organic compounds is carbon and Hydrogen. It belongs to group 14.
Which one of the following elements exhibit maximum number of valence electrons? [NCERT Exemplar](a) Na (b) Al (c) Si (d) P Answer: (d) Na (group 1) has one, A1 (group 13) has three (13 -10), Si (group 14) has four (14-10) and P (group 15) has five (15 – 10) valence electrons. Therefore, P has maximum number of valence electrons, i.e.3 (maximum among the given elements).
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? [NCERT Exemplar] (a) A, B, C (b) B, C, D (c) A, D, E (d) B, D, E Answer: (b) 2nd period contains elements with atomic number 3(Li), 7(N), 10(Ne). Since, 2nd period has elements having atomic number 3 to 10.
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? [NCERT Exemplar] (a) A and B (b) B and D (c) A and C (d) D and E Answer: (c)Electronic configuration of A (atomic number = 9) is 2, 7. Electronic configuration of B (atomic number = 11) is 2, 8,1. Electronic configuration of C (atomic number = 17) is 2, 8, 7. Electronic configuration of D (atomic number =12) is 2, 8, 2. Electronic configuration of E (atomic number =13) is 2, 8, 3. Elements which differ in atomic number by 8, i.e. 9 (A, fluorine) and 17 (C, chlorine) lie in the same group, i.e. group 17 (halogen).
In Mendeleev’s periodic table, gaps were left for the elements to be discovered later. Which one of the following elements found a place in the periodic table later? [NCERT Exemplar] (a) Germanium (b) Chlorine (c) Oxygen (d) Silicon Answer: (a) Mendeleev’s left some gaps in the periodic table for those elements which were not known at that time. Germanium element found a place in the periodic table later and Mendeleev’s predictions were found to be remarkably correct
Which of the following are the characteristics of isotopes of an element? [NCERT Exemplar] (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) Isotopes of an element have same atomic number and show same chemical properties.
Which of the following elements would lose an electron easily? [NCERT Exemplar] (a) Mg (b) Na (c) K (d) Ca Answer: (c) Electronic configuration of Mg (atomic number = 12) 2, 8, 2 Electronic configuration of Na (atomic number = 11)2, 8, 1 Electronic configuration of K (atomic number=19) 2, 8, 8, 1 Electronic configuration of Ca (atomic number =20) 2, 8, 8, 2 From the above electronic configurations, it is clear that K and Na will lose electrons easily to achieve a stable configuration. But out of K and Na, K will lose electrons more easily because the force of, attraction on the valence electron of K is least among the given elements.
Which among the following elements has the largest atomic radii? [NCERT Exemplar] (a) Na (b) Mg (c) K (d) Ca Answer: (c) Atomic radius increases on moving down in a group. Na and K are in the same group and K is below Na, so K will have a higher atomic radius, i.e. K > Na. In a period of moving left to right, the atomic radius decreases. Since K and Ca are in the same period and K is in the 1st group and Ca is in the 2nd group, so atomic radius of K will be more than Ca, i.e. K > Ca. Also, Na and Mg are in the same period, but Na belongs to the 1st group and Mg belongs to the 2nd group, so the atomic radius of Na is more than Mg, i.e. Na > Mg. Thus, if we take all these together we get K > Na >Mg and K > Ca > Mg. Hence, we can say that the atomic radius of K is the largest.
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. [NCERT Exemplar](a) Only (i) (b) (i), (ii) and (iii) (c) (i), (ii) and (iv) (d) Only (iv) Answer: (b) Only statement (iv) is correct. All the elements in the modern periodic table are arranged on the basis of their increasing atomic number. All the isotopes can be placed at one place in the same group of the periodic table.
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? [NCERT Exemplar] (a) Metal (b) Metalloid (c) Non-metal (d) Left-hand side element Answer: (c) Its outermost shell has 4 electrons. So, it is a non-metal. Non-metal forms acidic oxide and by sharing of electrons with halogen, it forms covalent halide.
Arrange the following elements in the order of their decreasing metallic character Na, Si, Cl, Mg, Al. [NCERT Exemplar] (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) Metals lie on the extreme left side of the periodic table. Metallic character decreases from left to right in a period. Na, Si, Cl, Mg, Al belong to the same period in the order Na, Mg, Al, Si, Cl. On moving in an i period from left to right, the metallic character decreases. Thus, the order of decreasing metallic character is: Na > Mg > Al > Si > Cl
Which of the following set of elements is written in order of their increasing metallic character? [NCERT Exemplar] (a) Be, Mg, Ca (b) Na, Li, K (c) Mg, Al, Si (d) C, O, N Answer: (a) Metallic character increases as we go down in a group.
Which one of the following does not increase while moving down the group of the periodic table? [NCERT Exemplar] (a) Atomic radius (b) Metallic character (c) Valence electrons (d) Number of shells in an element Answer: (c) Elements in each group has some number of valence electrons hence have same valency and thus exhibit similar chemical properties.
which of the following elements will form an acidic oxide? [NCERT Exemplar] (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) Non-metals form acidic oxides in general. Non-metals have 4 to 8 electrons in the outermost shell. The electronic configuration of given elements are (a) i.e. 7 = 2, 5 (b) i.e. 3 =2, 1 (c) i.e. 12 =2, 8, 2 (d)i.e. 19=2, 8, 8,1. So, element with atomic number = 7 (electronic configuration = 2, 5) with is non-metal (N) and it will form an acidic oxide. Rest three elements with atomic- numbers, 3 (Li), 12 (Mg) and 19 (K) are metals and hence, form basic oxides.
what type of oxide would Eka-aluminium form? [NCERT Exemplar] (a) EO3 (b) E3O2 (C) E2O3 (d) EO Answer: (c) Gallium has a valency of 3. Hence, it forms an oxide having the molecular formula E2O3. In other options, the valency of E is not 3.