What is the property of 16+31=31

We have the equation here is

16 + 31 = 31

When we simplify the equation to the understandable form, we move all terms or numbers to right and on left side zero will be left.

0 = 31-16-31

We get, 0 = - 16

Now we see that both sides of equations are not equal, it means there is no solution so it is an invalid equation.