dupal form: how to assign specific id to radio button using form api
If you need to assign IDs to each radio option, then you can use custom theme function, to theme your radios. See example:

$form['entry.497535900'] = array(
  '#type' =&gt; 'radios',
  '#title' =&gt; t('Category'),
  '#options' =&gt; array('P' =&gt;'Product','S' =&gt; 'Services','O' =&gt;'Others'),
  '#theme' =&gt; 'mymodule_custom_radios',  
);


The #theme parameter specifies function, which overrides the default radios styling function. You will need to define this function in hook_theme() and create the content of the function, where you can specify, how radios should be rendered.

/**
 * Implements hook_theme.
 */
function mymodule_theme($existing, $type, $theme, $path) {
  return array(
    'mymodule_custom_radios' =&gt; array(
      'arguments' =&gt; array('element' =&gt; NULL),
    ),
  );
}


Then create the content of this function.

function theme_mymodule_custom_radios($element) {
  // You can access all radios options like this - $element['#options'];

  $output = '';
  // ... create html output according to your needs
  return $output;
}