Answer
a) unchanged radius
b) statement 3
Work Step by Step
(a) We know that the radius of the daughter nucleus is the same as that of the original nucleus because the daughter nucleus has the same number of nucleons as contained in the original nucleus.
(b) We know that the best explanation is statement 3 -- that is, when a nucleus emits a beta particle, a neutron is converted to a proton but the number of nucleons is unchanged (and as a result, the radius of the daughter nucleus is the same as that of the original nucleus).
