Question

what is the mass number of an ion with 109 electrons 159 neutrons and a +1 charge? Express your answer as an integer

Answer 1

Z=atomic number (number of protons)
The number of protons is similar to the number of electrons when the atom doesn´t have charge. 
In this case :
"+1 charge" means that this atom would must have 1 electron more to be neutral, therefore the number of electrons of this element would be 109+1=110.

A=Z+N
A=mass number
Z=110 u
N=159 u

A=110 u + 159 u=269 u

Answer: the mass number (A) would be 269 u