A DDoS (Distributed Denial of Service) attack can disrupt the service of an IoT device by overwhelming it with a massive volume of traffic from multiple sources, causing it to become unreachable to legitimate users. DNS, HTTPS, and Malware are not types of attacks but rather components or protocols used in networking and security.

URLLC in 5G is essential for applications that require extremely low latency, such as autonomous vehicles, where split-second decisions are critical for safety.

One advantage of using predictive analytics in IoT for energy management is reduced energy consumption. By analyzing data from various sensors and devices, predictive analytics can optimize energy usage, helping to reduce energy waste and lower operational costs.

Machine Learning in IoT is primarily used for predictive analytics. It involves using historical data to make predictions and decisions, a key aspect of IoT applications.

For a medical wearable device requiring immediate response times, an RTOS is the best choice. RTOS is designed to handle real-time applications, making it ideal for critical functions. General-purpose, mobile, and network operating systems may not meet the stringent timing requirements of medical wearables.

Zero-Day attacks target vulnerabilities in IoT devices that are not yet known to the manufacturer or the public. Exploiting these undisclosed weaknesses can lead to unauthorized access or compromise of the device, making it a significant security concern.

FreeRTOS is a real-time operating system (RTOS) kernel that is event-driven and widely used in embedded systems due to its low resource requirements and real-time capabilities.

In advanced IoT applications involving autonomous vehicles and traffic signals, a Publish-Subscribe (Pub/Sub) communication model is most suitable. This model allows multiple devices (vehicles) to publish information (their status, location) to a central hub (traffic signals) and subscribe to updates from others. It's a scalable and efficient way for real-time interaction, enabling vehicles to receive timely traffic information.

Actuators in the context of IoT are devices that control and manipulate physical systems. They receive signals from a central controller or other IoT devices and perform actions like opening valves, turning motors, or adjusting settings to affect the physical world. They are essential for making automated decisions and responses in IoT applications.

Immutability is a core feature of blockchain technology. Once data is written to a blockchain, it cannot be altered retroactively, providing a tamper-proof record of information. Encryption, Decentralization, and Smart Contracts are relevant but serve different purposes.