Explanation:

The Purvanchal, or Eastern Highlands, is a mountain range in eastern India, comprising the Patkai-Bum, Naga Hills, Mizo Hills, and Manipur Hills. These are southward extensions of the Himalayas along India's eastern border, largely formed by the collision of the Indian plate with the Burma plate. We need to identify which of the given options does not belong to this group. \nOption (A) Mizo Hills: The Mizo Hills are located in Mizoram, forming part of the Purvanchal range. They are known for their parallel ridges and valleys. Therefore, this is a part of the Purvanchal. \nOption (B) Naga Hills: The Naga Hills are located in Nagaland and extend into Myanmar. They are a prominent part of the Purvanchal range, forming a natural boundary. Therefore, this is a part of the Purvanchal. \nOption (C) Patkai Hills: The Patkai Hills (or Patkai-Bum) are located on the India-Myanmar border, stretching across Arunachal Pradesh, Nagaland, Manipur, and Mizoram. They are the easternmost part of the Purvanchal range. Therefore, this is a part of the Purvanchal. \nOption (D) Jaintia Hills: The Jaintia Hills are part of the Meghalaya Plateau, located in the state of Meghalaya. Along with the Garo and Khasi Hills, they form a part of the Peninsular Plateau, which is an extension of the Deccan Plateau, not the Purvanchal (Himalayan extension). The Meghalaya Plateau is geologically distinct from the Purvanchal. Therefore, this option is correct as Jaintia Hills are not a part of the Purvanchal. \nIn conclusion, while Mizo, Naga, and Patkai Hills are integral components of the Purvanchal, the Jaintia Hills belong to the Meghalaya Plateau, which is a part of the older Peninsular Block of India.