<?php
$term = get_category(get_field('tag_1', $post->ID));
echo $term->name;
/*
stdClass Object
(
    [term_id] => 85
    [name] => Category Name
    [slug] => category-name
    [term_group] => 0
    [term_taxonomy_id] => 85
    [taxonomy] => category
    [description] =>
    [parent] => 70
    [count] => 0
    [cat_ID] => 85
    [category_count] => 0
    [category_description] =>
    [cat_name] => Category Name
    [category_nicename] => category-name
    [category_parent] => 70
)
*/
?>