Question

Which of the following is a radioisotope of Silicon?
A. $Si - 28$
B. $Si - 29$
C. $Si - 30$
D. $Si - 32$

Answer 1

Hint: Atoms that have an unstable neutron-proton ratio or a large amount of energy in their nucleus are known as radioisotopes also called radioactive isotopes. This is the condition for an atom to be radioactive, so we just have to see which of the given options will be an unstable one.

Complete step by step answer:
In nature, atoms are either stable or unstable. If the forces between the particles that make up the nucleus are balanced, an atom is stable. If these forces are imbalanced, or if the nucleus has a surplus of internal energy, an atom is unstable (radioactive).

Protons and neutrons exist side by side inside the stable nucleus. When the number of neutrons exceeds the number of protons, the nucleus becomes unstable, resulting in the conversion of a neutron into a proton and the emission of a beta particle. Then it's said that a nucleus is radioactive.By beta emission, $Si - 32$ decays to ${}^{32}P$ (which has a half-life of $14.28$ days) and finally to $Si - 32$.

So from the given options, option (D) $Si - 32$ is a radioisotope of Silicon. Hence is the correct answer.

Note: The three stable isotopes of silicon found in nature are \[^{28}Si{\text{ }}(92.23{\text{ }}percent)\],\[{}^{29}Si{\text{ }}(4.67{\text{ }}percent)\], and \[{}^{30}Si{\text{ }}\left( {3.10{\text{ }}percent} \right)\]with ${}^{28}Si$ being the most abundant. Twenty radioisotopes have been identified, with ${}^{32}Si$ having a half-life of $170$ years and ${}^{31}Si$ having a half-life of $157.3$ minutes being the most stable. The half-lives of the remaining radioactive isotopes are all less than seven seconds, with the majority of them being less than one-tenth of a second.