What determines the order of elements in today's periodic table?? btw for the subject it’s science but I had no option for it .

the atomic number (number of protons) order the elements.

Explanation: Each element on the Periodic Table has their own configuration of electrons. In order to have a neutral charge, there is an equal number of protons to electrons. Thus, the atomic number (number of protons) order the elements.

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the correct answer, according to e2020, is the second choice there is an occluded front in region a and a cold front in region b.