**Closure property**says that if for any two natural/whole numbers $a$ and $b$, $a∗b$ is also a natural/whole number then the set of natural/whole numbers is

**closed**under $∗$

where $∗$ represents $+,−,×$ or $÷$

Take any two natural/whole numbers $a$ and $b$, add them

So, we get $a+b∈N$/$W$.