Question

Which observation in alpha particle scattering experiment led Rutherford to make the conclusion that whole mass of an atom is concentrated in its centre.​

Answer 1

Conclusion of Rutherford's scattering experiment: Most of the space inside the atom is empty because most of the α-particles passed through the gold foil without getting deflected. Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space.

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Answer 2

Rutherford observed that every 12000th alpha was seemed to get deflected by small angles and some of them would get deflected by 180 degrees. This made him to know that most of the region of an atom is empty and most of the positive charge and mass of the atom is accommodated in small volume in the centre of the atom which we know as nucleus.