src/Helpers/Html.php
public static function radio($name, $checked = false, $options = [], $encoding = null)
    {
        static::processBooleanInputOptions($name, $options);
        return static::booleanInput('radio', $name, $checked, $options, $encoding);
    }
public static function radio($name, $checked = false, $options = [], $encoding = null)
    {
        static::processBooleanInputOptions($name, $options);
        return static::booleanInput('radio', $name, $checked, $options, $encoding);
    }
Generates a radio button input.
@param string $name the name attribute.
@param bool $checked whether the radio button should be checked.
@param array $options the tag options in terms of name-value pairs.
@param string $encoding
See [[booleanInput()]] for details about accepted attributes.

@return string the generated radio button tag