To answer this question, we need to understand the story of Mahishasura and the deity from whom he received the boon of immortality.
According to Hindu mythology, Mahishasura was a powerful demon who performed severe penance to please Lord Brahma. Impressed by his devotion, Lord Brahma appeared before Mahishasura and granted him a boon.
Mahishasura asked for the boon of immortality, but Lord Brahma refused to grant it. Instead, Lord Brahma offered him a different boon. Mahishasura asked that he could not be killed by any man or god. Lord Brahma granted him this boon, thinking that it was impossible for a woman to defeat him.
As a result, Mahishasura became almost invincible and unleashed havoc on Earth. The gods, unable to defeat him, sought the help of the divine Trinity - Lord Brahma, Lord Vishnu, and Lord Shiva.
In the battle that ensued, Mahishasura fought fiercely against the gods, but it was the goddess Durga, an incarnation of Goddess Parvati, who ultimately defeated him. Since Mahishasura had received the boon that he could not be killed by any man or god, Durga, being a goddess, was able to defeat him.
Therefore, the correct answer is:
B. Lord Shiva - This option is incorrect because Mahishasura did not receive the boon of immortality from Lord Shiva. It was Lord Brahma who granted him a different boon.