Question

Atom is not indivisible one observation

Answer 1

Any chemical reaction shows that electrons of atoms can break away or shared between two different atoms to get new molecules.

The simplest observation can be when you comb your dry hair (specially in winter) charge transfer take place to create imballance of charge, and visible attraction between hair and comb can be observed. This charge transfer occures because atom/molecules are divisible, so electrons can break apart.