Vector2 world_position = Camera.main.ScreenToWorldPoint(Input.mousePosition) as Vector2;

public class InventoryItem : Monobehaviour
{
   public Transform item_prefab;
   private void Start()
   {
      if ( item_prefab == null )
      {
          Debug.LogError("Item prefab is not valid.");
      }
   }
}

public void OnItemDrop(GameObject item)
{
   // Get world position
   Vector2 item_world_position = Camera.main.ScreenToWorldPoint(Input.mousePosition) as Vector2;
   // Get the prefab to instantiate
   Transform item_prefab = item.GetComponent<InventoryItem>().item_prefab;

   // Instantiate it to world position
   Instantiate(item_prefab, item_world_position, new Quaternion());

   // You can do this if you want your item sprite to disappear
   // Destroy(item);
}