'Mission Indradhanush' launched by the Government of India pertains to

1. A

   Immunization of children and pregnant women

   Immunization of children and pregnant women. Mission Indradhanush (2014) drives full immunisation coverage for unvaccinated and partially vaccinated children and pregnant women against seven (later expanded) vaccine-preventable diseases. That stored letter is the official key.

2. B

   Construction of smart cities across the country

   Smart cities. Smart Cities Mission is a separate urban programme. This letter is not the key.

3. C

   India's own search for the Earth-like planets in outer space

   Search for Earth-like planets. That is not Indradhanush; ISRO/NASA exoplanet work is unrelated. This letter is not the key.

4. D

   New Educational Policy

   New Education Policy. Education policy is not this mission’s mandate. This letter is not the key.

Summary. Official key is (a) immunization of children and pregnant women. Mission Indradhanush is a MoHFW catch-up vaccination drive, not smart cities, exoplanets or NEP. Honour the stored letter (a).