Question

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Answer 1

(1) valves are present in heart berween artrium and ventricles which prevent backflow of blood.
(2) gonorrhea and syphillis
(3) isotopes which were being classified on the basis of mass number was now classified on the basis of atomic number and so they were plqced together in the modern periodic law.
modern periodic law states that properties of elements are periodic functions of their atomic number.
(4) 10×2= 20cm far from pole.


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