Apex domains cannot have CNAME records.
Question and response
Question
dig ns.gov. NS
Answer
ns.gov. 5 NS danica.ns.cloudflare.com.
ns.gov. 5 NS otto.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0