he maximum acceleration that is tolerable for passengers in a subway train is 1.21 m/s2 and subway stations are located 810 m apart, what is the maximum speed a subway train can attain between stations

The answer is a 0.64 volts

An atom's smaller negative particles are at a distance from the central positive particles, so the negative particles are easier to move. 

Is there any opitions? if you have the periodic table, the noble gases are 8a family, the halogen are the 7a family, and the nonmetal are  carbon, nitrogen, phosphorus, oxygen, sulfur, selenium, fluorine, chlorine, bromine, iodine and astatine.