An important wildlife sanctuary in Nagaland, known for its Mithun population, is:

Singphan Wildlife Sanctuary
Ntangki National Park
Puliebadze Wildlife Sanctuary
Rangapahar Wildlife Sanctuary

The correct answer is: b) Ntangki National Park.

Ntangki National Park is a national park in Nagaland, India. It is located in the Tuensang district of the state, and is known for its population of mithun, a type of wild cattle. The park was established in 1975, and covers an area of 1,700 square kilometers. It is home to a variety of other wildlife, including tigers, leopards, elephants, and deer.

Singphan Wildlife Sanctuary is a wildlife sanctuary in Nagaland, India. It is located in the Wokha district of the state, and is known for its population of elephants. The sanctuary was established in 1989, and covers an area of 1,000 square kilometers. It is home to a variety of other wildlife, including tigers, leopards, deer, and birds.

Puliebadze Wildlife Sanctuary is a wildlife sanctuary in Nagaland, India. It is located in the Mokokchung district of the state, and is known for its population of tigers. The sanctuary was established in 1986, and covers an area of 500 square kilometers. It is home to a variety of other wildlife, including leopards, elephants, deer, and birds.

Rangapahar Wildlife Sanctuary is a wildlife sanctuary in Nagaland, India. It is located in the Dimapur district of the state, and is known for its population of elephants. The sanctuary was established in 1978, and covers an area of 1,500 square kilometers. It is home to a variety of other wildlife, including tigers, leopards, deer, and birds.