Phase 1: Understanding the Neolithic Era.
The Neolithic period is defined by the advent of agriculture, animal domestication, and the utilization of polished stone implements. These tools, crafted through grinding and polishing, enhanced efficiency in farming and other activities.
Phase 2: Evaluating the presented options.
- Option 1 (Polished and ground stone axes): This directly aligns with the Neolithic era, when early humans employed polished stone tools, such as axes, for diverse tasks, including agriculture.
- Option 2 (Stonehenge and sun worship): While these elements are associated with prehistoric cultures, they are not exclusive to the Neolithic culture within India. Stonehenge, for instance, lacks a connection to the Neolithic period in India.
- Option 3 (Increased use of blunt scrapers): Although scrapers were employed, the Neolithic period's primary emphasis was on polished tools.
- Option 4 (Invention of writing and poetry): Writing and poetry emerged significantly later and were not characteristic of the Neolithic period.
Phase 3: Determination. The definitive characteristic of the Neolithic period is the use of polished and ground stone axes.
Final Determination: \[\boxed{\text{The correct answer is (1) Polished and ground stone axes.}}\]