As per Mahabharata, whose son was Ghatotkacha?

Hidimba and Bhim

The correct answer is Option 1 - Hidimba and Bhim

Ghatotkacha was the name of the son of Hidimba and Bhim.

The Pandavas had fled into the forest. They were tired and fell asleep; only Bhima, the second Pandava, renowned for his prowess, was keeping watch. A man-eating rakshasa caught the scent of the Pandavas and sent his sister Hidimba to capture them. She fell in love with Bhima, transformed herself into a lovely maiden and proposed to him. He refused. Meanwhile, the rakshasa arrived and challenged Bhima to a wrestling match. Bhima accepted the challenge and killed him. The others woke up hearing the noise. Hidimba introduced herself, and declared her love for Bhima. She told Kunti: “I have forsaken my friends, my dharma and my kin; and good lady, chosen your tiger-like son for my man … whether you think me a fool, or your devoted servant, let me join you, great lady, with your son as my husband.” Ultimately, Yudhisthira agreed to the marriage on condition that they would spend the day together but that Bhima would return every night. The couple roamed all over the world during the day. In due course Hidimba gave birth to a rakshasa boy named Ghatotkacha. Then the mother and son left the Pandavas. Ghatotkacha promised to return to the Pandavas whenever they needed him.