What is the hard problem of consciousness, and what are some of the leading theories attempting to explain the relationship between mind and brain?

The hard problem of consciousness refers to the challenge of explaining how subjective experiences arise from physical processes in the brain. Leading theories include dualism, which posits a fundamental distinction between mind and matter, and various forms of monism, such as panpsychism and integrated information theory, which seek to explain consciousness as an emergent property of complex systems.