The periodic table was originally arranged according to

The periodic table was originally arranged according to their physical and chemical properties. This attempt was made by a German chemist in 1817. This attempt was followed by French and English chemists respectively. It was noticed by them that some elements had similar chemical properties and were in a group of three. However in the modern periodic table the elements are arranged according to their increasing atomic number which is equal to the number of protons in the nucleus of the atom of the element.

a and c

Explanation: