Quality Assurance in the Waterfall model is often considered rigid due to its linear and phase-dependent approach. In Waterfall, each phase must be completed before moving to the next, making it inflexible for changes or adaptations after each phase begins.

The primary objective of conducting a software audit is to ensure compliance with established processes and standards. Software audits help identify deviations from best practices and ensure that the software development process is in line with defined guidelines and standards. It's a critical aspect of quality assurance.

Corrective maintenance is about fixing errors or defects in the software. It addresses issues that may have been discovered during testing or reported by users and aims to restore the software's functionality.

The Single Responsibility Principle (SRP) states that a function or module should have one and only one reason to change, which means it should perform one specific job or responsibility. This helps in making the code more maintainable and understandable.

The Evolutionary model of software evolution focuses on making the software adaptable without altering its core functions. This approach often involves iterative development and incremental updates to enhance the software's functionality while maintaining its core features. It is a popular choice for software systems that need to evolve over time to meet changing requirements.

The Agile model emphasizes incremental development and testing, which allows for continuous revision and adaptation throughout the project. Agile projects break down work into small increments, and each increment is developed, tested, and revised, promoting flexibility and adaptability.

Violating the Liskov Substitution Principle (LSP) in a polymorphic system can lead to unexpected behavior and system issues. LSP states that subtypes must be substitutable for their base types without altering the desirable properties of the program. Violations can result in runtime errors or unexpected behavior, undermining the correctness and stability of the system.

Perfective maintenance involves making modifications to improve performance, enhance usability, or add new features to the software. It focuses on enhancing the software's functionality and user experience.

"Path" testing, a type of white box testing, ensures that every path in the code is executed at least once. It aims to cover all possible execution paths through the code to find potential issues.

In a Waterfall model, frequent changes in project scope can pose significant challenges to Quality Assurance. Since the requirements are expected to be well-defined upfront, any scope changes can lead to discrepancies between what was initially planned and what is being delivered, making it difficult to maintain quality standards.