Answer:
Krypton
Step-by-step explanation:
When arsenic forms an ion, it will try to resemble the structure of krypton. Most atoms always try to mimic the structure of the noble gases because this confers a very stable configuration on them.
Arsenic is an element with five electrons in its outermost shell. It will require just 3 more electrons to attain an octet.
This will make its structure resemble the noble krypton configuration.
The noble gases exists in uncombined form and they do not readily react with other elements.