Step 1:
Yan Sandhi occurs when vowels transform into semivowels like Ya, Va, Ra, or La.
Step 2:
In “Pratyeka”, the sound transformation involves the semivowel “Ya”.
Step 3:
Hence, the word demonstrates Yan Sandhi.
Step 4:
Therefore, the correct answer is:
\[
\boxed{\text{(3) Yan Sandhi}}
\]