The electron emitted in beta radiation originates from
A. inner orbits of atom
B. free electrons existing in nuclei
C. decay of a neutron in a nucleus
D. photon escaping from the nucleus

Hint: The beta radiation emission leads to the addition of one atomic number and no change in the mass number. This is because the beta emission is the process of addition of one electron and the conversion of neutrons to protons. Hence, the mass number stands the same but the atomic number increases.

Step by step solution:
(i) Radioactivity:
Radioactivity is defined as when a radioactive material reacts with the environment leads to emission of the higher energy with explosion. The energy emitted in the form of $\alpha $, $\beta $ and $\gamma $ decay.

(ii) Beta decay
Beta Decay is one of the radioactive decay in which a neutron is transformed into a proton or vice versa inside the nucleus of the radioactive element. The processes like beta and alpha decay allow the nucleus of the radioactive element to get as close as possible to the optimum neutron/ proton ratio. While doing this, the nucleus emits a beta particle which can either be an electron or positron. So, the beta decay may occur and either a proton can turn to a neutron or neutron to a proton. Electrons and the positron are emitted to balance charge in order to the law of conservation of charge. The beta decay occurs through the weak contact.

The example of beta decay is the decay of carbon-14 into nitrogen-14,
${}_6^{14}C\xrightarrow{{}}{}_7^{17}N + {e^ - } + {p^ + }$
Where, ${}_6^{14}C$ is carbon-14, ${}_7^{14}N$ is nitrogen-14, ${e^ - }$ is electron and ${p^ + }$ is proton.

Hence, the option (C) is correct.

Note: There are two types of beta decay, they are beta minus decay and beta plus decay. In beta minus decay, the neutron converts into an electron and proton and in beta plus decay, the combination of electron and proton leads to conversion to neutron. Hence, both the process is reversible.