What radioactive source did the Geiger and Marsden use in the scattering experiment?

The transition from the state $n = 3$ to $n = 1$ in a hydrogen like atom results in ultraviolet radiation. Infrared radiation will be obtained in the transition from

The transition from the state $n = 4$ to $n = 3$ in a hydrogen like atom results in ultraviolet radiation. Infrared radiation will be obtained in the transition

Choose the correct option from the following options given below

Given below are two statements:

Statement $I$: Atoms are electrically neutral as they contain equal number of positive and negative charges.

Statement $II$: Atoms of each element are stable and emit their characteristic spectrum.

In the light of the above statements, choose the most appropriate answer from the options given below.

A beam of fast moving alpha particles were directed towards a thin film of gold. The parts $A',\;B'$ and $C'$of the transmitted and reflected beams corresponding to the incident parts $A, B$ and $C$ of the beam, are shown in the adjoining diagram. The number of alpha particles in