Mission Indradhanush is a government initiative that aims to achieve full immunization coverage for all children in India. The name itself, "Indradhanush" which means "rainbow" in Hindi, signifies the broad range of vaccines that are being targeted under this mission.

Option 1, bullet train project, is unrelated to Mission Indradhanush. It is a separate initiative of the Indian government to introduce high-speed train services in the country.

Option 2, agriculture development, is also unrelated to Mission Indradhanush. While agriculture development is an important aspect of overall development in India, it is not the focus of this particular initiative.

Option 3, women empowerment, is once again unrelated to Mission Indradhanush. While women empowerment is a priority for the government and various initiatives have been launched to promote it, Mission Indradhanush specifically focuses on immunization.

Therefore, the correct answer is option 4, full immunization.