Option 1: Jawaharlal Nehru. Jawaharlal Nehru was a close associate of Mahatma Gandhi and played a significant role in the Indian independence movement. However, there is no evidence to suggest that he referred to Gandhi as the "Father of the Nation" for the first time.

Option 2: Sardar Vallabh Bhai Patel. Patel was also a prominent leader in the independence movement and played a crucial role in consolidating the princely states of India. However, there is no record of him using the term "Father of the Nation" for Gandhi.

Option 3: C. Rajagopalachari. Rajagopalachari was an Indian politician and freedom fighter. While he greatly admired Gandhi and worked closely with him, there is no proof of him using the title "Father of the Nation" for Gandhi.

Option 4: Subhash Chandra Bose. This is the correct answer. Bose, a fearless freedom fighter, referred to Gandhi as the "Father of the Nation" for the first time. He used this title to recognize Gandhi`s immense contribution to the Indian independence movement.

Alert - correct answer should be: There is no definitive evidence as to who first referred to Gandhi as the "Father of the Nation