The atomic number of an atom is always equal to the number of its
(1) protons, only(2) neutrons, only(3) protons plus neutrons(4) protons plus electrons

Which of the following is always a reactant in a combustion reaction? oxygen nitrogen hydrogen carbon

What is the molar mass of a gas that has density of 2.054 g/l

Two metal blocks that have slightly different temperatures are placed next to one another. after five minutes, they both have lower but equal temperatures. according to the law of conservation of energy, what  most likelyhappened? energy was created inside the blocks.energy was destroyed inside the blocks.energy was absorbed into the blocks from outside the system.energy was transferred from the warmer block to the cooler block.