A Greenfield city (or greenfield project) refers to development on previously undeveloped land, such as agricultural land or unused open areas. This contrasts with Brownfield development (on previously used, possibly contaminated land) or development within existing urban areas (infill, retrofitting, redevelopment).
A Smart City incorporates information and communication technology (ICT) and other means to enhance quality and performance of urban services, to reduce costs and resource consumption, and to engage more effectively and actively with its citizens.
India's Smart Cities Mission includes various types of projects, including retrofitting existing cities and developing greenfield areas.
Among the options provided:
(a) Bengaluru, (b) Mumbai, (d) Chennai: These are large, existing metropolitan cities (megacities). While they are part of the Smart Cities Mission and are undergoing various smart city projects (mostly retrofitting and redevelopment of specific areas), they are not "greenfield smart cities" in their entirety, as they are established urban centers.
(c) Naya Raipur (Atal Nagar): Naya Raipur (officially Atal Nagar-Nava Raipur) is the new capital city of Chhattisgarh, planned and developed as a greenfield city. It has been designed from the outset with smart city principles and infrastructure. It is often cited as one of India's first (or one of the most prominent examples of) planned greenfield smart cities. It incorporates modern urban planning, green building concepts, smart transportation, and ICT-enabled services.
Therefore, Naya Raipur is known for being a significant greenfield smart city development in India.
\[ \boxed{\text{Naya Raipur}} \]