The density of water is equal to 1.0 g/cm3. a substance with density equal to 0.9 g/cm3 would in water.

Float
Explanation: Since water density is 1, substances whose density is less than 1 will float while those whose density is less than 1 will sink.
The more the density of the substance approaches 1, the less part will appear above the water level. Scientist discovered that the density of the substance tell exactly where the substance will be placed.
Example, a substance with density 0.1 then 10% will be below the water line while if the density of the substance is 0.9 then 90% of the substance will be below the water line.

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.