Question

India is federal in form but unitary in spirit explain it

Answer 1

India was declared as a Union of States, by the Constitution. Though it is similar to federal but not exactly federal. Nowhere in the constitution the word federal is mentioned.

Indian Union is based more on a 'holding together federation' than a 'coming together federation'

The Indian states cant opt out of the Union just like in a federation. Unlike USA which is a federation, the the central govt in India is much more powerful than the Provincial governments. Also India has a single constitution whereas USA states have their own constitutions. 

India is more like a Canadian Federation than USA federation. The states in US came together and formed a country whereas India formed states after the country got freedom.