Knowledge hub

 1. Mr. Lakshman, aged 65 years worked as a civil engineer in a construction company. He had to walk and climb a lot as part of his job. After retirement, he settled with his son spending time with his grandchildren. Now a days he is experiencing difficulty in doing certain chores which involves physical movement.  (i) Which of the following tests would you recommend to check Mr. Lakshman’s fitness? (a) Harvard step test  (b) Rikli & Jones test (c) AAHPER test (d) Rock port test (ii) How many series of tests are there in the prescribed fitness test for Mr. Lakshman? (a) 8  (b) 6 (c) 5  (d) 4 (iii) Chair sit & reach test is done to check ____________ (a) Agility (b) Speed (c) Flexibility (d) Strength (iv) Pick the odd one out. (a) Arm curl test (b) Chair stand test (c) 6 min walk test (d) Partial curl up (v) The 8 foot up &go test, as shown in the picture is performed to assess _________ (a) Agility (b) Endurance (c) Speed (d) Strength 2. (i) Both the...

               1. Introduction The Periodic Table as it stands today and the Modern Periodic Law. We will also learn how the periodic classification follows as a logical consequence of the electronic configuration of atoms. Finally, we shall examine some of the periodic trends in the physical and chemical properties of the elements.    WHY DO WE NEED TO CLASSIFY ELEMENTS ? We know by now that the elements are the basic units of all types of matter. In 1800, only 31 elements were known. By 1865, the number of identified elements had more than doubled to 63. At present 118 elements are known. Of them, the recently discovered elements are man-made. Efforts to synthesise new elements are continuing. With such a large number of elements it is very difficult to study  individually the chemistry of all these elements and their innumerable compounds individually. To ease out this problem, scientists searched for a systematic way to...

                                                     Chapter - 1 Chemical Reactions and Equations Multiple Choice Questions  1. Which of the following is not a physical change?  (a) Boiling of water to give water vapour  (b) Melting of ice to give water  (c) Dissolution of salt in water  (d) Combustion of Liquefied Petroleum Gas (LPG)  Soln: Answer is (d) Combustion of Liquefied Petroleum Gas (LPG)  Explanation: Combustion is always a chemical change because new compound is formed after burning and it is irreversible. 2. The following reaction is an example of a 4NH3 (g) + 5O2 (g) → 4NO(g) + 6H2O(g)  (i) displacement reaction  (ii) combination reaction  (iii) redox reaction  (iv) neutralisation reaction  (a) (i) and (iv)  (b) (ii) and (iii)  (c) (i) and (iii)  (d) (iii) and (iv)...

  Diagonal Relationship between Beryllium and Aluminium The ionic radius of Beryllium (Be 2+) is estimated to be nearly 31 pm; the charge/radius ratio Or e/m ratio is nearly the same as that of the Al 3+ ion. Hence beryllium resembles aluminium in these ways. Some of the similarities are given below: » Like Aluminium, Beryllium(be) is not readily attacked by acids H+ donor because of the formation of an oxide film on the surface of the metal by reacting with oxygen, i.e. they are rendered passive by nitric acid. » Beryllium hydroxide[[Be(OH)4]2] dissolves in excess of alkali to give a beryllate ion, [ Be(OH)4]2– just as aluminium hydroxide[Al(OH)3] gives aluminate ion, [Al(OH)4] » The chlorides of metals beryllium and aluminium have Cl– bridged chloride structure in vapour phase. Both the chlorides are soluble in organic solvents and are strong as Lewis acids They are used as Friedel Craft catalysts. » Beryllium(Be) and aluminium(Al) ions have strong tendency to form complexes, (Be...