Answer :
The answer is (3) decay. An atom whose nucleus is unstable is said to be "radioactive," and its nucleus undergoes nuclear decay.
Answer: The nucleus of radium-226 is unstable and hence undergoes decay.
Explanation: Radium has many isotopes. One of them is [tex]_{88}^{226}\textrm{Ra}[/tex] which has 88 protons and 138 neutrons. It is a radioactive isotope and undergoes decay process.
This isotope undergoes alpha - decay and produces Radon-222 isotope.
Equation for alpha - decay follows:
[tex]_{88}^{226}\textrm{Ra}\rightarrow _{86}^{222}\textrm{Rn}+_2^4\alpha[/tex]
Hence, the nucleus of radium-226 undergoes decay process.
