Which of these is correct please help

What is the result of multiplying (2.5 × 1010) × (2.0 × 10-7)? a. 5.0 × 103 b. 5.0 × 10-3 c. 5.0 × 1017 d. 5.0 × 10-17

What is the subscript for oxygen in its molecular formula

Moseley made revisions to the periodic table that resolved some of the problems with mendeleev's version. which of thesewas a result of his revisions to the periodic table? the revised periodic table could account for the discovery of new elements.the revised periodic table could account for variations resulting from isotopesscientists could begin to write new information onto each element.scientists could begin to place the table on a single sheet of paper.