Answer:
The equation that correctly describes the decay is :
Ra ----->
Rn +
He
Step-by-step explanation:
When the solid radium start decaying in order to form the radon gas, it starts losing two protons with one neutron. The two neutron as well as one proton together forms an alpha particle, hence a type of radiation is formed. Also we know that radon itself is radioactive as it also leads to the decay, after that it loses an alpha particle and also form an element called as polonium. Radium being the most stable form of isotope, radium 226, also holds a half life of 1600 years. It will decay into radon 222 through the alpha decay or can also lead 212 by ejecting a carbon 14 nucleus.