Let's look at the available options and see what can and can't be reversed or undone.
tying shoelaces
* This is pretty simple, you can tie some shoelaces, untie them, and repeat as many times as you want. So this is a reversible physical change.
filing nails
* When you file nails, you start with one large nail and end up with a smaller nail plus a lot of "nail dust". If you wanted to reverse that process, you'd somehow have to convert that "nail dust" you created back into original nail. And that's not possible. You might be able to glue the dust back on, but that would result in a mixture of glue and nail dust, not original nail. So this is not a reversible physical process.
cracking an egg
* Once again, it's easy to crack an egg. Not so easy to then uncrack it and end up with an undamaged egg. So I wouldn't call this process reversible either.
cutting hair
* So for each hair you start out with a long piece of hair, then you cut it into 2 or more shorter lengths. You might be able to glue those pieces back together, but that wouldn't result in a piece of uncut hair, it would instead result in several pieces of hair glued together. So this process isn't reversible either.
So of the 4 available choices, only tying shoelaces is reversible.</span>
