Question

When alpha particles are sent through a thin metal foil, only one out of ten thousand of them rebounded. This observation led to the conclusion that

• A. Positively-charged particles are concentrated at the centre of the atom
• B. More number of electrons is revolving around the nucleus of the atom
• C. The unit positive charge is only present in an atom
• D. A massive sphere with a more negative charge and unit positive charge is present at the centre of the atom

Answer 1

The correct option is A

Positively-charged particles are concentrated at the centre of the atom

Postulates of Rutherford's atomic model: Based on the observations of the alpha scattering experiment, Rutherford postulated that:

1. Most of the space in the atom is empty.
2. The positive charge and the mass of the atoms are concentrated in a very small volume. He termed this region, the nucleus.
3. Negatively charged electrons move around the nucleus in circular orbits.
4. As the nucleus is positively charged and the electrons are negatively charged, they are held together in an atom by electrostatic forces.

The explanation for the correct option: (A)

1. Most of the mass and all the positive charge of an atom are concentrated in a very small region at the centre of the atom known as the nucleus.
2. When alpha particles are sent through a thin metal foil, only one out of ten thousand of them rebounded due to the presence of a nucleus at the centre.

The explanation for the incorrect option:

(B) When alpha particles are sent through a thin metal foil, only one out of ten thousand of them are rebounded not due to the number of electrons revolving around the nucleus of the atom as electrons do not repel alpha particles.

(C) It is not the unit positive charge present in an atom that causes the rebounding of alpha particles sent through a thin metal foil.

(D) There is not just a unit of positive charge,, there is a region in which positive charge is present.

Hence, the correct option is (A).