Read the following passage and answer the questions.
In 1911, H. Geiger and E. Marsden did a scattering experiment suggested by Rutherford. A radioactive source of \({}^{214}_{83}\mathrm{Bi}\) gave out alpha-particles of energy 5.5 MeV. The alpha-particles passed through lead bricks and then fell on a gold foil. The foil was only \(2.1\times10^{-7}\ \mathrm{m}\) thick. A detector made of a zinc sulphide screen and a microscope was placed near the foil. The detector could be turned around the foil. The whole apparatus was kept in a vacuum chamber. An alpha-particle carries a positive charge \(2e\). A gold nucleus carries a positive charge \(Ze\), with \(Z = 79\) for gold. The graph below shows the number of scattered alpha-particles detected at different scattering angles.
Which of the following is/are correct about the scattering experiment and the graph shown?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → All of the above
Option (1) Many of the α-particles pass through the gold foil without undergoing any deflection. — Incorrect. This statement is true. But it is not the only true statement here.
Option (2) Very few, only about one in 8000, are scattered by more than \( 90^\circ \). — Incorrect. This statement is also true. It too is only part of the full answer.
Option (3) The solid curve depicts the prediction of Rutherford’s nuclear model. — Incorrect. This statement holds as well, so choosing it alone leaves out the other two.
Option (4) All of the above — Correct. All three statements hold:
In Rutherford’s nuclear model, the positive charge and most of the mass sit in a tiny nucleus. The nucleus is 10,000 to 100,000 times smaller than the atom. So most α-particles go straight through the foil without any collision, and (1) holds.
An α-particle is turned through a large angle only when it comes close to a nucleus. Such close approaches are rare. So only about 1 in 8000 is deflected beyond \( 90^\circ \), and (2) holds.
In the figure, the dots are the measured data points. The solid curve is the theoretical prediction for an atom with a small, dense, positive nucleus, so (3) holds.
NCERT (2026-27):
Alpha-particle Scattering and Rutherford’s Nuclear Model of Atom – “… The dots in this figure represent the data points and the solid curve is the theoretical prediction based on the assumption that the target atom has a small, dense, positively charged nucleus. Many of the α-particles pass through the foil. It means that they do not suffer any collisions. Only about 0.14% of the incident α-particles scatter by more than 1°; and about 1 in 8000 deflect by more than 90°.”