What is the mass number of an ion with 109 electrons, 159 neutrons, and a 1 charge?

It is not specified whether charge is +1 or -1.
If charge is  +1,  then total no. of electrons is 110,and so is atomic number.
Mass No.=No. of neutrons+ Atomic Number                       (1) 
               =159+110=269
If Charge is -1, total no.of electrons= 108= atomic number
From (1)
Mass No.= 159+108=267

Hope It Helped :)

Elias is almost correct. he just got it backwards.the correct answer is that it demonstrates elastic potential energy transforming into kinetic energy.