Which missing item would complete this beta decay reaction?

For us to understand the missing item that would complete beta decay reaction, we need to achieve in depth understanding of chemical formulas and nuclear symbols. Next is to have great comprehension of the following points:
1.) Neutron in nucleus breaks down and changes into a proton.
2) Then it emits an electron, as well as an anti-neutrino which go into space.
3) Lastly, atomic number continuously goes UP while mass number remains unchanged.

Ibelieve your answer is b.hope this : )