Why there is a huge Change in SERP's when we change IP?

Google searches are typically targeted for the market indicated by the client IP address. The Google server that responds to the query is also usually located closer to the client so you're getting a response from a server in India when using an IP address in India and from one in the US when using a US IP address. Searches are ranked by frequency of hits recorded locally so an unpaid listing (or a bargain priced one) will show higher in India than in the US if most of the hits are from India.