**Core Concept**
The Integrated Child Development Services (ICDS) is a government program aimed at improving the nutritional and health status of vulnerable groups, including children, pregnant women, and lactating mothers. In rural areas, the administrative unit plays a crucial role in implementing and managing the ICDS project.

**Why the Correct Answer is Right**
The Community Development Block (CDB) is the administrative unit responsible for implementing the ICDS project in rural areas. This is because the CDB is the smallest administrative unit at the sub-district level, comprising multiple gram panchayats. The CDB is responsible for planning, coordinating, and monitoring the ICDS activities at the grassroots level. This includes identifying and targeting the most vulnerable populations, mobilizing community participation, and ensuring the effective delivery of ICDS services.

**Why Each Wrong Option is Incorrect**
**Option A:** PHC (Primary Health Centre) is a healthcare facility that provides basic medical care, but it is not the administrative unit responsible for implementing the ICDS project. While PHCs may be involved in providing ICDS services, they do not have the administrative authority to oversee the project.

**Option C:** Zilla Parishad is a district-level administrative body responsible for overall development and administration of the district. While it may have a role in overseeing the ICDS project at the district level, it is not the administrative unit responsible for implementing the project at the rural level.

**Option D:** Gram Panchayat is a local self-governing body at the village level, responsible for providing basic amenities and services to the village. While gram panchayats may be involved in implementing ICDS services at the village level, they do not have the administrative authority to oversee the project.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the ICDS project is implemented at the grassroots level, and the Community Development Block is the key administrative unit responsible for its implementation. This highlights the importance of community participation and local-level administration in effective program implementation.

**✓ Correct Answer: B. Community development block**