The correct answer is option 1, Shashi Tharoor. He is the author of the book "Pax Indica: India and the World of the 21st Century".

Option 2, Salman Khurshid, is not the correct answer. He is a Indian politician and author, but he is not the author of the book in question.

Option 3, S.M. Krishna, is also not the correct answer. He is a Indian politician and former Minister of External Affairs, but he is not the author of this particular book.

Option 4, Pranab Mukherjee, is also not the correct answer. He was the President of India, but he is not the author of this book either.

It is important to note that while Shashi Tharoor is the confirmed author of the book "Pax Indica: India and the World of the 21st Century", it is always a good idea to verify the information from reliable sources to ensure accuracy.