What particle in an atom determines what element it is?

I need a refresher.

Brad and his family like to go camping. they always take a gas lantern with them. the lantern can take fiuels but always puts out the same amount of light. brad has two different kinds of fuel for the lantern. how can he figure out which kind of fuel has more chemical energy that the lantern can turn into light? measure the brightness of the lantern using each kind of fuel by comparing it to the full moon. g measure the volume of the containers of fuel. measure how long the lantern stays lit on a fixed amount of fuel. measure the mass of each container of fuel using a balance scale. answer 12

Two nitro no2 groups are chemically bonded to a patch of surface. they can't move to another location on the surface, but they can rotate (see sketch at right). it turns out that the amount of rotational kinetic energy each no2 group can have is required to be a multiple of ε, where =ε×1.010−24 j. in other words, each no2 group could have ε of rotational kinetic energy, or 2ε, or 3ε, and so forth — but it cannot have just any old amount of rotational kinetic energy. suppose the total rotational kinetic energy in this system is initially known to be 32ε. then, some heat is removed from the system, and the total rotational kinetic energy falls to 18ε. calculate the change in entropy. round your answer to 3 significant digits, and be sure it has the correct unit symbol.

Which factor is likely to impact the possible number of compounds ?