The price elasticity of demand measures how responsive the quantity demanded of a good is to a change in its price. Goods that are more necessary or have fewer substitutes tend to have less elastic demand, while goods that are more luxury or have more substitutes tend to have more elastic demand. 1) A blue colored iPhone: This is a very specific good with many substitutes (other colors of iPhones, other brands of smartphones). Therefore, its demand is likely to be very elastic - a small change in price could lead to a large change in quantity demanded. 2) A smartphone: This is a broader category of goods, but there are still many substitutes (different brands, different models). Therefore, its demand is likely to be somewhat elastic, but less so than the blue colored iPhone. 3) iPhone: This is a specific brand of smartphone, and while there are substitutes (other brands), they may not be perfect substitutes for consumers who prefer the iPhone's specific features or brand reputation. Therefore, its demand is likely to be the least elastic of the three. So, from most elastic to least elastic, the ranking would be