Which of the following statements about intelligence is correct ?

The correct option is Intelligence is multi-dimensional and a set of complex abilities.

Understanding Intelligence:
Intelligence is a multifaceted cognitive capability that encompasses the ability to learn, reason, solve problems, adapt to new situations, and think abstractly. Modern psychological theories, such as Howard Gardner's Theory of Multiple Intelligences and Robert Sternberg's Triarchic Theory, highlight that intelligence cannot be reduced to a single, fixed capacity or measured entirely by a single score.

Evaluating the Options:
1. "Intelligence is a fixed ability determined at the time of birth only." - This statement is incorrect because intelligence is influenced by both genetic factors and environmental experiences (such as education, culture, and exposure). It is dynamic and can develop over time.
2. "Intelligence can be accurately measured and determined by using standardized tests." - Standardized tests (such as IQ tests) measure specific cognitive skills like logical reasoning and verbal abilities, but they fail to capture creativity, emotional intelligence, practical problem-solving, and socio-cultural skills.
3. "Intelligence is a unitary factor and a single trait." - Earlier theories (like Spearman's general intelligence factor 'g') suggested a unitary aspect, but modern educational psychology recognizes that intelligence consists of distinct domains rather than a single uniform trait.
4. "Intelligence is multi-dimensional and a set of complex abilities." - This statement is correct. It acknowledges that individuals possess diverse skills, capacities, and talents across various domains (linguistic, mathematical, spatial, musical, interpersonal, etc.).

Therefore, intelligence is best described as a complex, multi-dimensional set of abilities.