which of the following is the correct way to print the  slug property

Choose correct from the following

which of the following is the correct way to print the  slug property of $fisrtTag object in this code snippet?
$tags=wp_get_tags($post->ID);
$firstTag=$tags[0];

  1. $fistTag->slug
  2. $fistTag.slug
  3. $fistTag[0][‘slug’]
  4. $fistTag[‘slug’];

The right answer is :

$fistTag->slug