CBSE Class 9 Answered

(a) Chlorine occurs in nature in two isotopic forms with masses 35 u and 37 u in the ratio of 3:1. Calculate the average atomic mass of chlorine atom on the basis of this data. (b) Give two uses of isotopes. (c) Illustrate any two observations of Rutherford's model. OR(a) Explain why elements have fractional atomic masses.(b)What are nucleons?(c) Helium atom has atomic mass 4 and has 2 protons in its nucleus. How many neutrons does it have?

Asked by Topperlearning User | 19 Mar, 2015, 10:55: AM

Expert Answer

$begin mathsize 12px style left parenthesis straight a right parenthesis space The space isotopes space of space Chlorine space are space in space the space ratio space 3 colon 1. space It space means space that space the space two space isotopes space are space 75 % space and space 25 % space respectively. Average space atomic space mass space of space chlorine space equals space fraction numerator 35 space straight x space 75 space over denominator 100 end fraction plus space fraction numerator 37 space straight x space 25 space over denominator 100 end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space 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space space space space equals space 35.5 space straight u left parenthesis straight b right parenthesis space Uses space of space isotopes colon space space space space space space space left parenthesis straight i right parenthesis space An space isotope space of space cobalt space used space in space the space treatment space of space cancer. space space space space space space space left parenthesis ii right parenthesis space An space isotope space of space iodine space is space used space in space the space treatment space of space goiter. space space left parenthesis straight c right parenthesis space left parenthesis straight i right parenthesis space Most space of space the space straight alpha minus particles space passed space straight space through space the space gold space foil. space space space space space space space left parenthesis ii right parenthesis space One space out space of space 12 comma 000 space particles space appeared space to space rebound. space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space OR space space left parenthesis straight a right parenthesis space The space elements space have space fractional space atomic space masses space due space to space the space existence space of space isotopes. space straight e. straight g. space chlorine space has space two space isotopes space Cl presubscript 17 presuperscript 35 space and space space Cl presubscript 17 presuperscript 37 space and space are space present space in space the space ratio space of space 3 colon 1. space space Hence comma space space Average space atomic space mass space of space chlorine space equals fraction numerator space 35 space straight x space 75 over denominator 100 end fraction space plus space fraction numerator 37 space straight x space 25 over denominator 100 end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals fraction numerator space 105 over denominator 4 end fraction space plus space fraction numerator 37 space over denominator 4 end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space fraction numerator 142 space over denominator 4 end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space 35.5 space straight u space space left parenthesis straight b right parenthesis space Protons space and space neutrons space reside space in space the space nucleus space of space an space atom space and space are space thus space called space nucleons. space Since comma space mass space of space an space atom space is space due space to space protons space and space neutrons space only comma space nucleons space give space the space mass space of space an space atom. space This space is space called space mass space number. space space left parenthesis straight c right parenthesis space Mass space number space of space helium space is space equal space to space its space atomic space mass space but space has space no space units. space space space space space space Hence comma space Mass space number space of space helium space equals space 4 space space space space space space space space space space space space space space space space space No. space of space protons space in space the space nucleus space equals space 2 space space space space space space space space space space space space space space space space space Atomic space number space of space the space element space equals space 2 space space space space space space space space space space space space space space space space space No. space of space neutrons space equals space 4 space minus 2 space equals space 2 end style$ Answered by | 19 Mar, 2015, 12:55: PM