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1 The three elements A, B and C with similar properties have atomic masses X, Y and Z, respectively. The mass of Y is approximately equal to the average mass of X and Z. What is., ‘such an arrangement of elements called as? Give one example of such a set of elements., , Elements have been arranged in the following sequence on the basis of their increasing atomic, masses,, , F, Na, Mg, Al Si, P, S, Cl, Ar, K, (a) Pick two sets of elements which have similar properties., , (b) The given sequence represents which law of classification of elements?, Can the following groups of elements be classified as Dobereiner's triad ?, (@) Na, Si, Cl, , (0) Be, Mg, Ca, , 2.Atomic mass of Be 9; Na 23; Mg 24; Si 28; C135; Ca 40,, , Explain by giving reason., , 3.1n Mendele’ ev 's Periodic Table the elements were arranged in the increasing order of their, atomic masses. However, cobalt with atomic mass of 58.93 amu was placed before nickel, having an atomic mass of 58.71 amu. Give reason for the same, , 4.Hydrogen occupies a unique position in Modern Periodic Table”. Justify the statement., , 5.Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by, Mendele’ ev., , 6.Three elements A, B and C have 3, 4 and 2 electrons respectively in their outermost shell. Give, the group number to which they belong in the Modern Periodic Table. Also, give their valencies., , 7.if an element X is placed in group 14, what will be the formula and the nature of bonding of its, chloride?, , ‘8.Compare the radii of two species X and Y. Give reasons for your answer., (@) X has 12 protons and 12 electrons, , (0) Y has 12 protons and 10 electrons