Social psychology, organisational theory, and psychology are all part of the mix of behavioural sciences informing organisational behaviours. These fields provide valuable insights into human behavior, group dynamics, and organizational structures. However, systems theory is not typically considered a part of the mix of behavioural sciences informing organizational behaviors.

Explanation:

Social psychology: Social psychology is the scientific study of how individuals think, feel, and behave in social situations. It examines the influence of social factors on individual behavior and the interactions between individuals within groups or organizations. Social psychology provides valuable insights into topics such as leadership, motivation, communication, and decision-making within organizations.

Organisational theory: Organisational theory is the study of how organizations function and operate. It explores various aspects of organizations, including their structure, culture, strategy, and behavior. Organizational theory helps in understanding factors that influence organizational effectiveness, such as leadership styles, organizational change, and employee motivation.

Psychology: Psychology is the scientific study of human behavior and mental processes. It encompasses a wide range of sub-disciplines, including cognitive psychology, developmental psychology, and industrial-organizational psychology. Psychology provides insights into individual behavior, personality, motivation, perception, and learning, which are all important in understanding and predicting organizational behaviors.

Systems theory: Systems theory, on the other hand, is a general theory that focuses on the interrelationships and interactions between different components within a system. While systems theory can provide a framework for understanding organizations as complex systems, it is not typically considered a part of the mix of behavioral sciences informing organizational behaviors. Instead, systems theory is often used in fields such as engineering, biology, and ecology to study complex systems and their dynamics.

In conclusion, the correct answer is option C: Systems theory as it is not typically considered a part of the mix of behavioral sciences informing organizational behaviors.