Which of these would a mechanical engineer do?

I dont see the answers

Explanation:

Mechanical engineers design power-producing machines, such as electric generators, internal combustion engines, and steam and gas turbines, as well as power-using machines, such as refrigeration and air-conditioning systems. Mechanical engineers design other machines inside buildings, such as elevators and escalators.

Explanation:

it means there are 3 atoms of oxygen

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.