Important questions of periodic classification of elements

A.     MULTIPLE CHOICE QUESTIONS

1.    If two members of a Dobereiner triad are calcium and barium, then the third member of the triad is

    (a)Magnesium

    (b)Strontium

    (c)Caesium 

    (d)Sodium

        2.   An element which is an essential constituent of all organic compounds belong to:

            a .   Group 1

       b.   Group 14

        c.   Group 15

       d.  Group 16

       3.      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<C<O<Be<Li

              d.  (iv)F<O<Be<C<Li 

        FILL IN THE BLANKS

       4.      Barium belongs to the same group as that of Magnesium so the formula of barium nitrate and magnesium sulphate is                                                     and                    .

       5.      Property used by Mendeleev to classify elements in his periodic table was .-------

       6.      The Modern Periodic Table consists of   periods  and     groups.

      ONE MARK QUESTIONS

       7.      Name the two elements that have two electrons in their outer most shells.

      8.      Name  the  element having  electronic  configuration 2,8,2.

       9.      The law of octaves was applicable up to which element.

        ASSERTIONS AND REASONS

      For the question numbers 10, 11 and 12, two statements are given- one labelled Assertion

     (A) and the other labelled Reason (R) . Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:     

(a) Both A and R are true and R is the correct explanation of A.

    (b) Both A and R are true but R is not the correct explanation of A.

     (c) A is true but R is false.

     (d) A is false but R is true.

       10.    Assertion: Li, Na, K form Doberiners triads

            Reason: Atomic mass of Na is roughly the average of the atomic mass of Li and K.

       11.    Assertion: Silicon is a metalloid.

            Reason: Silicon shows properties of only non- metals.

      12.   Assertion: Magnesium belongs to the 3rd period of the modern periodic table.

           Reason:   The valence electrons of magnesium are two. 

     THREE MARK QUESTIONS

       13.  (a)The atomic radius of hydrogen is 37pm. Express it in meters. 

             (b)How does atomic size vary in a group and a period?

              (c)If an element has an atomic number 18, mention the group to which it belongs.

       14. (a)An element has an electronic configuration 2, 8, 6. Explain its position in the periodic table.   

         (b)The size of the sodium atom is bigger than that of the hydrogen atom. Why?

          (c)Which has a greater atomic size-Cl or Br?

ELECTRIC MOTOR

 ELECTRIC MOTOR

  It works on the principle that when a current-carrying conductor is  placed in a magnetic field it will experience a force on it.

It consists of the following parts:-

1. Armature ABCD 

2. Field magnets N and S                                           

3. Split rings P and Q                                  

4. Brushes X and Y

      When a current is allowed to flow through the coil ABCD by closing the switch, the coil starts rotating in anti-clockwise direction. This happens because of a downward force acts on arm AB and at the same time, an upward force acts on  arm CD. The direction of forces can be  found by using Fleming’s left hand rule. As a result, the coil rotates in anti-clockwise direction.

      After half a rotation, the position of AB and CD gets interchanged  so the direction of current in the coil ABCD gets reversed. hence the half-ring P comes in contact with brush Y and half-ring Q comes in contact with brush Y.

      The speed of rotation of motor can be increased by:-

(i)            Increasing current through armature

(ii)          Increasing number of turns in the coil of armature

(iii)        Increasing area of the coil.

(iv)        Increasing strength of the magnetic field.

 Q 3.1: What kind of energy transformation takes place in an electric motor:-

           (a) Electrical energy into chemical energy

           (b) Electrical energy into light energy 

           (c) Mechanical energy into electric energy

           (d) Electrical energy into mechanical energy.

Q3.2. State YES or NO:-

Statement	Responses
(i)            Fleming’s left hand rule is used to find the direction of force	Yes/no
(ii)          Electric motor works on the principle of Electro Magnetic Induction	Yes/no

 

Q 3.3. Will there be any change in the direction of rotation of the armature of motor when position of both the poles (N and S)  are interchanged? Give your reply with proper explanation.

…………………………………………………………………………………………………………………………………………………………………………………………

Answer 

3.1

 Full Credit:-Option (d)

 No Credit:- For any other responses.

  3.2

Full Credit:- 

(i) Yes  (ii)No    

Answer: 3.3

 Full credit :-Direction of rotation of electric motor will change in opposite direction .It will rotate in clockwise direction because of opposite directions of forces on the arms AB and CD according to Fleming’s left hand rule due to change in direction of magnetic field.

Partial credit:-  Opposite direction

 No credit:- For any other response or  wrong responses.

 

Chemical reaction and equations Quiz- 1

Chemical reactions and equations

Quiz

 

1. An element ‘X’ displaces iron from the aqueous solution of iron sulphate. List your observations if the element ‘X’ is treated with the aqueous solutions of copper sulphate, zinc sulphate and silver nitrate. Based on the observations arrange X, Zn, Cu and Ag in increasing order of their reactivities.
   1.   Ag < Cu < Zn < X
   2.   Ag < Cu > Zn < X.
   3.   Cu < Zn < X< Ag
   4.   X<Cu < Zn < Ag
2. Reaction of 'magnesium' with air is
   1.   Exothermic reaction
   2.   Endothermic reaction
   3.   Reversible reaction
   4.   Substitution reaction
3. In writing chemical equations, inclusion of state symbols shall be done while
   1.   Correct chemical formulae of reactants and products are written
   2.   The equation is being balanced to fulfill the law of conservation of mass
   3.   The equation has been balanced
   4.   The chemical formulae of products and reactants have been changed to bring about quick balancing
4. The reaction in which two compounds exchange their ions to form two new compounds is called
   1.   Displacement reaction
   2.   Combination reaction
   3.   Double displacement reaction
   4.   Redox reaction
5. On immersing an iron nail in CuSO₄ solution for a few minutes, you will observe
   1.   No reaction takes place
   2.   The color of solution fades away
   3.   The surface of iron nails acquire a black coating
   4.   The color of solution changes to green
6. Which of the given statements is not a physical change?
   1.   Boiling of water to give water vapour
   2.   Melting of ice to give water
   3.   Dissolution of salt in water
   4.   Combustion of Liquefied Petroleum Gas (LPG)
7. In which of the given, heat energy will be evolved?
   1.   Electrolysis of water
   2.   Dissolution of NH₄Cl in water
   3.   Burning of L.P.G.
   4.   Decomposition of AgBr in the presence of sunlight
8. When crystals of lead nitrate are heated strongly in a dry test tube
   1.   Crystals immediately melt
   2.   A brown residue is left
   3.   White fumes appear in the tube
   4.   A yellow residue is left
9. Paheli Is Writing Some Statement Which Is Given By Her Teacher. Would You Help Him To Choose The Incorrect Statements?
   1.   The combustion reaction of candle wax is characterized by a change in state from solid to liquid and gas.
   2.   When a chemical reaction absorbs heat energy, then the temperature of reaction mixture is falls and it becomes cold.
   3.   When a Zinc metal reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas.
   4.   None of the above.
10. Which Of The Following Statement Is Or Are Incorrect?
    1.   The burning of magnesium in air to form magnesium oxide.
    2.   The properties of the product magnesium oxide are entirely different from the reactants.
    3.   The chemical reaction between sodium carbonate and dilute
    4.   None of the above
11. Magnesium ribbon is rubbed before burning because it has a coating of
    1.   basic magnesium carbonate
    2.   basic magnesium oxide
    3.   basic magnesium sulphide
    4.   basic magnesium chloride
12. Which of the following statements about the given reaction are correct?
    3Fe (s) + 4H2O (g) → Fe3O4 (s) + 4 H2 (g)
    (i) Iron metal is getting oxidised
    (ii) Water is getting reduced
    (iii) Water is acting as reducing agent
    (iv) Water is acting as oxidising agent
    1.   (i), (i) and (iii)
    2.   (i) and (iv)
    3.   (i), (ii) and (iv)
    4.   (ii) and (iv)
13. MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
    Identify the substance oxidized in the above equation.
    1.   MnCl2
    2.   HCl
    3.   H2O
    4.   MnO2
14. A substance ‘X’ is used in white-washing and is obtained by heating limestone in the absence of air. Identify ‘X’.
    1.   CaOCl2
    2.   Ca (OH)2
    3.   CaO
    4.   CaCO3
15. Select the oxidising agent for the following reaction:
    H2S + I2 → 2HI + S
    1.   I2 (Iodine)
    2.   H2S
    3.   HI
    4.   S