Firewall rules can be used to enable access for traffic to specific ports or services. “Service numbers” is rather stilted English but you may encounter these types of wordings on the actual exam –don’t let them confuse you.
“Only unauthorized application port or service numbers” is incorrect. Unauthorized ports/services would be blocked in a properly installed firewall rather than permitting access.
“Only authorized application port or ex-service numbers” is incorrect. “Ex-service” numbers is a nonsense term meant to distract you.
“Only authorized application port or service integers.” While service numbers are in fact integers, the more usual (and therefore better) answer is either service or “service number.”
References CBK, p. 464 AIO3, pp. 482 – 484