Question

In Rutherford’s $\alpha$- rays scattering experiment, gold foils are used because of:
(A) High malleability
(B) Ductility
(C) High melting point
(D) High ionisation energy

Answer 1

In scattering experiment,Rutherford wants foils to be as this as possible. As gold is metal ,check the properties of metals which satisfies this condition and with this correct answer should be predictable.

Complete answer: The significance of the experiment is that it gave people a clear idea of what an atomic model is and what is the structure of an atom. It was first assumed that atoms had a plum-pudding structure. The positive charge is distributed throughout and the negative charge( electrons) are embedded in it.
However, Rutherford with his experiment of gold foils cleared this misconceptions of that time. The radioactive element was used as $\alpha$- particle source which decays and emits $\alpha$- rays. A beam of particles was scattered and focussed on very thin gold foil.
He observed the following things –
1. A number of rays crossed the foil undeflected.
2. Some of the rays bounced back to almost $180^\circ$.
3. And a large number of rays deflected at large angles from their paths.
He drew the following conclusions-
That atom must be mostly empty space. The fact that some of the alpha-particles bounced back, there must be a very dense centre ( which later was known as nucleus) . Some of the particles deflected because of the repulsive forces , so there must be charged particles present. This was Rutherford's scattering experiment.
He used gold foil in his experiment because he wanted the foil to be as thin as possible. Since gold is malleable in nature , it can be drawn into thin sheets .The malleability is the property of metal by virtue of which it can be beaten into thin sheets. Gold foil was used for that purpose only.

Hence , the correct option is (A).

Note: The alpha-particle is actually a He-nucleus. It has 2 units of positive charge and 4 units of mass. The fast moving particles have some energy and can penetrate through matter to some extent and hence they are used.