what is balancy

I think you are asking about valency.

valency of an atom is defined as the capacity of an atom to combine with same or different element to attain a fully filled outermost shell.

for example in case of Mg it's atomic no. is 12

it's electronic configuration is 2,8,2

it will loose two e^- to get the stable configuration that is 2,8

hence valency of Mg is 2.

you will get to know more about this in class ninth.