The correct option is (a).
Explanation
Ernest Rutherford’s alpha-particle scattering experiment (1911) was pivotal in determining the internal structure of the atom. By bombarding a thin gold foil with high-energy alpha particles, Rutherford challenged the existing "plum pudding" model proposed by J.J. Thomson and established the nuclear model of the atom.
Statement-wise Analysis:
- Statement 1 is Correct: In the experiment, it was observed that the vast majority of alpha particles passed through the gold foil without any deflection. This observation led to the conclusion that most of the space inside an atom is empty, allowing particles to pass through unhindered.
- Statement 2 is Incorrect: Only a small fraction of alpha particles were deflected by small angles. This indicated that the positive charge is not distributed over the entire volume of the atom (as suggested by Thomson). Instead, the positive charge is concentrated in a very small volume relative to the total size of the atom.
- Statement 3 is Incorrect: A very tiny fraction of alpha particles (approximately 1 in 20,000) rebounded back by 180 degrees. This observation suggested that nearly all the mass of the atom is concentrated in a dense central core (the nucleus), rather than being distributed evenly throughout the atomic volume.
Key Takeaway:
Rutherford's model characterizes the atom as mostly empty space with a tiny, dense, positively charged nucleus at the center, which contains nearly all of the atom's mass.