Step 1: Concept Clarification: The query requires the identification of a specific mural situated on an external wall of Kala Bhavana, Visva-Bharati University's fine arts department in Shantiniketan. This institution is recognized for its substantial impact on modern Indian art, featuring several notable public murals.
Step 2: Detailed Analysis: Kala Bhavana's external walls display multiple significant murals by distinguished artists. The mural in question is a sand-cast cement artwork on the facade of a studio building, executed by the renowned artist K.G. Subramanyan and finished in December 1988. It portrays three mythological goddesses: Durga, Manasa, and Kamala Kamini. This piece is differentiated from Subramanyan's later, more recognized black-and-white mural at the same site. Consequently, option 4's title and year correctly identify this particular artwork.
Step 3: Conclusion: The mural on the exterior wall of Kala Bhavana, Shantiniketan, is titled 'Three mythological goddesses' and was completed in 1988.