Jhum, also known as shifting cultivation, is a traditional agricultural practice where people cut down the vegetation of an area, burned them, and then start farming on this land. This method is predominantly practiced in the north-eastern states of India.

Option 1: Manipur does have an area under Jhum cultivation, but it`s not more than 50% of the state`s total area. Therefore, the answer provided is incorrect.

Option 2: In Assam, Jhum cultivation was practiced primarily in hilly terrains but it doesn`t account for 50% of the state`s total area.

Option 3: In Sikkim, due to the terrain and climatic conditions, the area under Jhum cultivation isn`t significant.

Option 4: Mizoram is the state where over half of the total area is under Jhum cultivation. The steep slopes of the hills and the tribal population`s dependency on agriculture contribute to this.

Alert - the correct answer should be 4, Mizoram.