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.

assuming that your periodic table has eighteen columns, you should highlight   the four elements in the third column from the left of the table.

explanation

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the have energy higher than those in the orbital while lower than those of the orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the orbital is therefore filled right after orbitals and before orbitals.  

potassium has electron configuration and calcium . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the and should be highlighted as well.

You would do 1500/4 and the answer is 375