Which of the following is not a reason that power plants are unable to achieve 100 percent efficiency? a. entropy increases. b. the amount of work obtained from a process never has work needing to go into it. c. heat is often a waste product. d. not all energy is converted heat from chemical reactions into useful work.

I think it might be A but I'm not 100% sure.  Sorry if I'm wrong

I believe it's A. Entropy increases.

For cyclohexane compounds drawn in a chair conformation:   -axial bonds are vertical  -equatorial bonds are parallel to two bonds within the ring.  thus, as i assume the chair conformation is drawn:   -the x group is in an axial position, as are the five other vertical bonds.  -three axial bonds are on the top face of the ring  -the other three axial bonds are on the bottom face  the position of the second substituent on each ring carbon is equatorial.  gauche groups must be on an adjacent carbon such as carbon 6 and carbon 2, and also gauche groups are rotated by 60 degrees relative to each other.  drawing the newman projections for c1–c2 and c1–c6 aids in visualizing the groups that are gauche to the y group on c1.  click this link and watch some academic videos that may you more understand the topic