Your laboratory instructor has given you two shiny, light-gray metal cylinders. your assignment is to determine which one is made of aluminum (d = 2.699 g/ml) and which one is made of titanium (d = 4.54 g/ml).

One of the ways that we will be able to distinguish between the metals given that they have the same characteristic of being shiny and light-gray, is to density difference. 

It is known that a substance whose density is larger than the density of the liquid to which it is submerged, will sink in the fluid. Also, the solid whose density is smaller compared to that of the fluid will float. 

In most ideal case, we may opt to prepare a solution with density of 3 g/ml. Since aluminum has density lower than 3, it will float in the fluid. The titanium will sink on it because of a density higher than or greater than 3. 

It is to be noted that pure water cannot be used because its density is 1 g/ml and both metals will sink in it. 

Most likely a is the answer - because  you generate   38 atp's but also consume an atp.   each atp gives approx. less than 4 kcal so probably a is the closest answer.