position of hydrogen:since hydrogen has the least atomic number i.e 1 ,it is kept in group 1 of modern periodic table, but still controversial due to its. dual characteristics since it shows the characteristics of borh group 1 and group 17.
position of isotopes :isotopes are element having the same atomic number but different atomic weight . Without any doubt all isotopes of one element and kept in one place.
position of lanthanide and acnitinides: element of Lanthanides series and element of Actinides series are kept below the main block of the periodic table as they have different properties from other elements.
correction of periodic law: some elements do not obey mendeleev periodic law , but when they are arranged according to atomic number they obey the modern periodic law.
position of alkali metals and coinage metals : in modern periodic table , alkali metal are kept in group IA and coinage metals are in group.

hope this helped you☺️

any confusion then comment it and let me know.

actually as I say these points say that the modern periodic table is better than mendeleev periodic table so, don't get confused.

3 0

3 years ago

zubka84 [21]

The answer is A. the solar ultraviolet ray breaks the molecule apart

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3 years ago