The scientist referred to in the question is indeed Linus Carl Pauling, hence option 2 is the correct answer. Here`s why each option either fits or does not fit the clues given in the question:

1. G.N. Lewis: Although Lewis had substantial contributions in the field of chemistry, especially in the concept of chemical bonding, he did not focus on biology or promote Vitamin C.

2. Linus Carl Pauling: The only person to have won two unshared Nobel Prizes (in Chemistry and Peace), Pauling definitively worked in the intersection of physics, chemistry, and biology. He was a strong advocate of the health benefits of Vitamin C, even controversially promoting it as a treatment for cancer.

3. Fritz London: London made significant contributions to quantum mechanics and theoretical chemistry. However, he was not known to have combined different scientific fields in a unifying way, nor did he advocate for the use of Vitamin C.

4. Walter Heitler: Heitler, a physicist known for his work on quantum mechanics, did not venture into biology. He also did not advocate for Vitamin C as a medical treatment.

In summary, only Linus Carl Pauling matches all the descriptions given in the question.