Question

When a gold sheet is bombarded by a beam of $\alpha $-particles, only a few of them get deflected whereas most go straight, undeflected. This is because
A. The force of attraction exerted on the $\alpha $-particles by the oppositely charged electrons is not sufficient.
B. A nucleus has a much smaller volume than that of an atom.
C. The force of repulsion acting on the fast-moving $\alpha $-particles is very small.
D. The neutrons in the nucleus do not have any effect on the $\alpha $-particles.

Answer 1

Hint: Consider Rutherford’s gold foil experiment which concluded that the atom is mostly an empty space with a comparatively tiny, massive, positively charged nucleus in the centre. Size of an atom is ${{10}^{-10}}$meters while the size of a nucleus of an atom is ${{10}^{-15}}$meters.

Complete step by step solution:
The above-mentioned question actually states about Rutherford's gold foil experiment.
So, let us first know what is Rutherford's gold foil experiment and what did he conclude from his experiment.
So, Rutherford’s gold foil experiment changed the way of thinking about the atomic structure explained by Thomson.
In the gold foil model or alpha-particle scattering, Rutherford directed beams of alpha particles at thin gold foil and concluded that the atom was mainly an empty space with the nucleus at the centre and electrons revolving around it. When the particles were fired towards the foil, he saw that one in twenty thousand particles underwent a change in direction of motion of more than ninety degrees and the rest particles deviated from the path by a small margin. So, this concluded that an atom consisted of empty space with most of the mass at the centre in small volume. This centre was later named as nucleus.
So, from the above experiment, we can say that most of the alpha particles went undeflected because of the small volume of the nucleus.

Hence, the correct option is B.

Note: Rutherford’s gold foil experiment further gave an opportunity to calculate the mass and size of the nucleus. It also concluded that nucleus which is the centre of an atom, is usually of positively charged and has a small volume and size compared to the atom.