A radio (role) is used for a checkable element when a group of elements are available and only one among them can be checked at a time. All the similar radio elements can be grouped and assigned with radiogroup role. A radio role is owned by radiogroup role.
Usually a radio role is assigned when elements contain few checkable options. Options such as yes or no, male or female, morning, noon, evening or night etc can be assigned with radio role. If the options are more such as states of a country a combobox role should be assigned.