The primary objective of Unit Testing is to verify the correctness of individual units or components of a software system. It focuses on ensuring that each unit functions as intended and produces the expected output. Unit Testing is not primarily concerned with identifying design flaws, performance issues, or user satisfaction.

In API development, the acronym CRUD stands for Create, Read, Update, and Delete. The "Update" operation refers to modifying or changing existing data in the system.

The selection of inappropriate software quality metrics can pose risks to the accurate evaluation of a software project because it may lead to incorrect conclusions about the software's quality. Using irrelevant or inadequate metrics may provide a false sense of security or concern, potentially impacting project planning, resource allocation, and overall quality assessment.

The Capability Maturity Model Integration (CMMI) is a well-known software quality standard that provides a framework for managing and controlling software quality. It defines maturity levels and process areas to guide organizations in improving their software development processes.

In the software development life cycle (SDLC), the planning phase is where the high-level view of the project is established, and its goals are determined. This phase involves defining the scope, objectives, and requirements of the project.

Utilizing risk-based testing reduces the number of test cases while focusing on the most critical areas of the software. This approach improves effectiveness by ensuring high-risk areas are thoroughly tested and efficiency by saving time and resources on less critical parts.

In an Agile model, the use of iterative development cycles allows for continuous testing and quality assurance throughout the project. This helps identify issues early, respond to changes, and ensure that the product aligns with quality standards, even when facing tight deadlines.

Availability is the quality attribute that reflects the software's ability to perform its required functions under stated conditions for a specified period of time. This attribute is crucial for ensuring that the software is accessible and operational when needed.

Preventive maintenance aims to avoid future issues by proactively identifying and resolving potential problems before they impact the software. This helps in reducing the likelihood of defects and improving long-term software reliability.

In a Waterfall model, where requirements are well-understood and not expected to change, the Quality Assurance phase can benefit from in-depth and comprehensive testing. Since the entire project is developed in a sequential manner, the focus can be on thorough testing to ensure the product meets quality standards.