This is a Plain Tiger butterfly (Danaus chrysippus) also known as African monarch is found throughout India. These butterflies are toxic in nature , similar to their well known relative the monarch butterfly found in North America(Danaus plexippus). The caterpillars of these butterflies feed on toxic plants belonging to Asclepiadaceae family which contains toxic cardenolides. This is the reason that birds and invertebrates don’t feed on these butterflies.
They advertise their toxicity by having bright body colouration which is termed as “Aposematism ” and so they are called Aposematic butterflies.