1 candy bar costs 1.25, 2 candy bars cost 2.50, 3 candy bars cost 3.75, 4 candy bars cost 5.00, and 5 candy bars cost 6.25. The proportional relationship between the cost and quantity for candy bar 2 is represented by the equation y=x. Which candy bar is cheaper the cheapest cost per bar?

The equation y=x represents a proportional relationship with a constant of proportionality equal to 1. So, the cost of candy bar 2 is equal to its quantity (x).

Based on the given information, we can see that the cost of candy bar 2 is the same as its quantity for all quantities.

Therefore, candy bar 2 is the cheapest cost per bar because its cost is equal to its quantity.