Explanation:

The word 'ताकि' (Taki) is a समुच्चयबोधक अव्यय (subordinating conjunction) that connects two clauses, indicating purpose or result. In the given sentence, it links 'खूब मन लगाकर पढ़ो' (study diligently) with 'परीक्षा में प्रथम आओ' (come first in the exam), meaning 'study diligently so that you come first in the exam.'