मराठी व्याकरणात इ, उ, ऋ या बद्दल अनुक्रमे य्, व्, र् असे आदेश होतात. त्यांना _____ म्हणतात.

The correct answer is Option C (यणादेश).

Key Points:
• यणादेश (Yanadesha): When dissimilar vowels follow इ/ई, उ/ऊ, or ऋ, they change respectively to the semi-vowel consonants य्, व्, and र् (उदा. प्रीति + अर्थ = प्रीत्यर्थ, मनू + अंतर = मन्वंतर, पितृ + आज्ञा = पित्राज्ञा).
• Option 3 (यणादेश).
• When इ, उ, ऋ become य्, व्, र् respectively, the substitution is called 'यणादेश'.
• संप्रसारण is the exact inverse process (when semi-vowels य्, व्, र्, ल् change into vowels इ, उ, ऋ, लृ in roots). Therefore, the process stated in the question is unambiguously यणादेश.
• Key Takeaway: The replacement of इ, उ, ऋ with य्, व्, र् is known as यणादेश; the reverse process is संप्रसारण.