Loss of a beta particle
a) converts a neutron into a proton
b) has no effect on the nucleus
c)converts a proton into a neutron
d) causes the atomic number to decrease by 2
e) causes the mass number to decrease by four

When a beta particle is emitted from the nucleus the nucleus has one more proton and one less neutron. This means the atomic mass number remains unchanged and the atomic number increases by 1.
We can also say that beta decay is a type of radioactive decay in which a proton is transformed into a neutron inside an atomic nucleus.

a) converts a neutron into a proton

The earths magnetic field revolves around it's magnetic poles.