Correct Answer: The emigration of skilled individuals from one country to another.

Solution : The correct answer is (a) The emigration of skilled individuals from one country to another.

The concept of "brain drain" refers to the phenomenon where highly skilled and educated individuals emigrate from their home country to another country in search of better opportunities, higher salaries, or improved living conditions. This emigration of talented individuals can result in a loss of valuable human capital for the home country and a gain for the destination country.

Brain drain is often a concern for developing countries as they may invest in educating and training individuals who then choose to leave and contribute their skills and knowledge elsewhere. This can have negative effects on the development and growth of the home country's economy, as the loss of skilled individuals can hinder innovation, research, and overall productivity.

The term "brain drain" is commonly used in the context of migration and labor market dynamics, particularly with regards to the movement of highly skilled professionals such as doctors, engineers, scientists, and academics.