By using the example, which of the following laws may be demonstrated?

if a and b are rational numbers, then a + b = b + a.

According to the commutative law of addition if a and b are two rational numbers then the order in which they are added will not change their sum. 

For example, if a and b are two rational numbers then, a+b = b+a.

Therefore the given example demonstrates the commutative law of addition.

A glance at other option

• Example of associative law of addition: (a+b)+c= a+(b+c)
• Example of distributive law of addition: a(b+c)=ab+ac
• Example of Closure property: a+b=c