The correct answer is option 4, which states that Mission Indradhanush aims at full immunisation of children.

Option 1, reducing child deaths due to pneumonia, is not the primary objective of Mission Indradhanush. While immunisation can help reduce the incidence of pneumonia, the mission`s main focus is on achieving full immunisation coverage.

Option 2, reducing the impact of rotavirus, is also not the main objective of Mission Indradhanush. While rotavirus vaccination is included in the mission`s immunisation schedule, the aim is to provide comprehensive immunisation to children for a wide range of preventable diseases, not just rotavirus.

Option 3, elimination of maternal tetanus, is a separate goal of the government`s immunisation programs but is not specifically targeted by Mission Indradhanush. Maternal tetanus elimination is achieved through the provision of tetanus toxoid vaccinations during antenatal care and postnatal care visits.

Therefore, option 4, full immunisation of children, is the correct answer as it aligns with the primary objective of Mission Indradhanush.