A) Pods in the same namespace can resolve each other by their hostname. This is generally true. Kubernetes assigns a hostname to each Pod, and DNS within the cluster allows pods in the same namespace to find each other using these hostnames.
B) A ClusterIP Service is resolvable by its name within the same namespace. This is correct. Kubernetes creates a DNS entry for each ClusterIP Service, making it resolvable by its name within the namespace it resides in.
C) To resolve a Service in a different namespace, the full FQDN is required. This is also correct. To access a Service in another namespace, you typically need to use its fully qualified domain name (FQDN), which follows the format <service-name>.<namespace-name>.svc.<cluster-domain>.
D) Resolving a Headless Service name returns a single IP address of one of its Pods. This is incorrect. When you resolve the name of a Headless Service, the DNS server returns multiple IP addresses, corresponding to all the Pods that are part of that Service. This is the key difference between Headless and ClusterIP Services in terms of DNS resolution.