Question

Bombardment of Beryllium by alpha particles resulted in discovery of:
A. Proton
B. Nucleus
C. Neutron
D. Position

Answer 1

Hint: In this problem we will discuss the discovery of a certain particle after bombardment of beryllium by alpha particles and the theory and history behind this discovery with earlier experiments which lead to this conclusion.

Complete solution:
In the earlier times until 1932 before the discovery of neutrons by Sir James Chadwick , atoms were known to consist of positively charged protons surrounded by negatively charged electrons around it, to make it neutral and stable. Maximum part of the atom is empty and mass is concentrated in the nucleus.

But, after some years scientists soon realized that the atomic model offered by Rutherford is not complete, because from many experiments it is predicted that the mass of the nucleus is twice the number of protons and this extra mass caused a disturbance in the Rutherford model. So the existence of some neutral particles having mass similar to that of protons was suggested but at that there was no experimental proof because at that time experiments for only charged particles was possible.

In 1932, when James repeated the experiments at the Cavendish Laboratory by bombardment of beryllium by alpha particles, he observed the emission of a neutral particle with mass equal to proton and they called it neutron.
$\begin{array}{c}9\\ 4\end{array}Be+\begin{array}{c}4\\ 2\end{array}\alpha \to \left[\begin{array}{c}12\\ 6\end{array}C\right]+\begin{array}{c}1\\ 0\end{array}n$

$\therefore$ On bombardment of beryllium by alpha particles resulted in discovery of Neutrons hence, option (C) is correct.

Note:
During the experiment the main question arose how massless photons can eject protons which are heavier than electrons so the ejected rays after the bombardment of beryllium cannot be photons which leads to further discoveries and at last theory behind the neutrons was discovered.