A battery used in a mechanical toy stores 10,000 kJ of energy. The toy 5 points expends 7,500 kJ of energy before the battery runs out of energy. What is
the efficiency of the system?

In chemistry, the type of an atom (what element it is) is determined by: a) the number of protons it contains in its nucleus.b) the number of neutrons it contains in its nucleus.c) the number of protons it has in a cloud around the nucleus.d) the number of neutrons it has in a cloud around the nucleus.e) the number of electrons it exchanges with its neighbors.