Answer : 3. "Capable"
Explanation :

The most appropriate synonym for "competent" is "capable." "Competent" and "capable" both imply having the necessary skills, knowledge, or ability to perform a task effectively. The other options, such as "complex" (intricate), "poor" (lacking in skill or ability), and "beginner" (novice), have different meanings and do not convey the same idea of proficiency and capability as "competent" does.