Concept:The phrase "brain drain" means the departure of educated or skilled professionals from one country to another, driven by better opportunities.
Explanation:The underlined idiom in the sentence is "brain drain."
It specifically refers to the migration of talented individuals like scientists, doctors, and engineers.
The primary reason for this movement is the search for better career prospects, higher salaries, advanced facilities, or an improved quality of life.
In the given sentence, it means Indian scientists are leaving for other countries seeking these advantages.
Option A ("higher studies") is not the core meaning, as brain drain typically involves already-qualified professionals moving for work, not study.
Option C ("security") could be a factor but is not the primary or most common driver.
Option D ("excursion") suggests a temporary trip, which contradicts the long-term or permanent nature of brain drain.
Therefore, the correct interpretation is "movement for better prospect."
Answer:Movement of professionals to another country for better prospect