The mass number of a nucleus (except hydrogen) is:

always less than its atomic number
never less than its atomic number
sometimes equal to its atomic number
sometimes less than and sometimes more than its atomic number

An exothermic reaction is conducted in an insulated calorimeter filled with water. the calorimeter is then sealed so that there is no heat exchanged between the contents of the container and the surrounding air. which of the following statements is true about the reaction?

Asample of aluminum foil contains 8.60 × 1023 atoms. what is the mass of the foil?

Asubstance is a good conductor of electricity which of the following best explains a probable position of the substance in a periodic table