The correct answer is c) Maintenance of law and order.
Panchayati Raj institutions are local self-government institutions in India. They are responsible for a wide range of functions, including preparation of development plans, tax collection, implementation of welfare schemes, and maintenance of law and order. However, in Arunachal Pradesh, the maintenance of law and order is a function of the state government. This is because Arunachal Pradesh is a hilly state with a large tribal population, and the state government has decided that it is better for the state police to be responsible for law and order in the state.
The other options are all functions of Panchayati Raj institutions in Arunachal Pradesh. Preparation of development plans is a function of the Gram Panchayat, while tax collection is a function of the Zilla Parishad. Implementation of welfare schemes is a function of both the Gram Panchayat and the Zilla Parishad.
Panchayati Raj institutions are important for democracy and development in India. They provide a platform for local people to participate in decision-making and to hold their elected representatives accountable. They also help to improve the delivery of services to the people.