Write down the mass number

answer=
a. Al: atomic number= 13
mass number= 27
proton=elektron=atomic number= 13
neutron=mass number-atomic number= 14

b. Cl: atomic number= 17
mass number= 36
proton=elektron=17
neutron=36-17= 19

c. K: atomic number=19
mass number=39
proton=elektron=19
neutron= 39-19= 20