Answer
The daughter nuclide is $~~^{40}_{20}Ca$
Work Step by Step
During $\beta -$ decay, a neutron decays into a proton and also releases an electron and an electron antineutrino. Therefore, in the daughter nuclide, the total number of nucleons stays the same, but the number of protons increases by one.
The daughter nuclide has 40 nucleons and 20 protons. The element with 20 protons in the nucleus is calcium.
We can write the symbol for the daughter nuclide:
$^{40}_{20}Ca$
