How is the modern periodic table arranged? a. by increasing atomic number b. by increase in atomic mass c. by increasing atomic size d. by decreasing atomic number

The modern  periodic table is  arranged  by increasing   atomic  number  (answer  A)

    Explanation

 A  periodic table  is a chart  that contain chemical element   arranged in order of increasing  atomic  number.

The vertical   column  of periodic table is called  group. It contain  element with similar  properties. on the other hand horizontal  row  is  called  period.for  example is group 1  which contain  element  such as hydrogen, lithium  and potassium. This  element in group 1 are arranged in order of increasing atomic number  down the group  that  is  from hydrogen which is in atomic number 1 ,followed by lithium  which is atomic number 3   and  then potassium  which is atomic number 19.

And a) oxygen i believe