If a nucleus undergoes beta particle emission

Question

a. its atomic number decreases by four and its mass number decreases by two.
b. its atomic number decreases by two and its mass number decreases by four.
c. its atomic number increases by one and its mass number is unchanged.
d. its atomic number decreases by one and its mass number increases by one.
e. its atomic number is unchanged and its mass number decreases by one.

Answer is D

Answer 1

nope.
And example for element X and I'll make up numbers.
24/12X ==>beta + Y
24/12 X ==> 0/-1 e + zYw and you want to know what z and w are.
The upper numbers add up on both sides. The lower numbers add up on both sides.
upper number first. 24 = 24 + ? so w must be 0
lower number next. 12 = -1 + ? so ?(or z) must be 25.
You can see that the lower number increases by 1 and the upper number stays the same.