Use the `disabled` attribute to disable an input radio.

```html
<sd-radio-group label="Disabled radio in group" value="1">
  <sd-radio value="1">Radio 1</sd-radio>
  <sd-radio value="2" disabled>Radio 2</sd-radio>
  <sd-radio value="3">Radio 3</sd-radio>
</sd-radio-group>
```