can anyone help me with this?

Question

"the principle which underlies the checking of the balance of equations using base quantities"

Answer 1

Conservation of ________________

What goes in the blank depends on what is meant by "base quantities."

If it's a matter of balancing atoms and charges (chemistry stuff), then it's conservation of mass. Or it could be conservation of energy, conservation of momentum, conservation of angular momentum, etc.

Maybe the answer is just "conservation."