In Uttar Pradesh, which ancient Buddhist pilgrimage centre marks the place where Gautama Buddha attained Mahaparinirvana?

The correct answer is Kushinagar.

Explanation:
Gautama Buddha, the founder of Buddhism, attained Mahaparinirvana (the final death/liberation of an enlightened soul) at Kushinagar, located in the modern-day state of Uttar Pradesh, India. According to Buddhist scriptures, at the age of 80, Lord Buddha entered Parinirvana under a pair of Sal trees in Kushinagar after delivering his final teachings to his disciples.

Overview of the Other Options:
• Sarnath: Located near Varanasi, Uttar Pradesh, Sarnath is where Buddha delivered his first sermon, an event known as Dharmachakra Pravartana (Turning the Wheel of Law).
• Vaishali: Located in Bihar, Vaishali is where Buddha preached his last sermon before traveling to Kushinagar.
• Rajgir: Located in Bihar, Rajgir was an important royal capital where Buddha spent several retreat seasons and where the First Buddhist Council was convened after his death.