A rational number in its decimal expansion is 2.125. It is Terminating rational number. 

Given rational number is 2.125 which can be written in the form of $\frac{p}{q}$(where p and q are co-prime integers and q is non-zero). 

So, it becomes $\frac{2125}{1000}$. 

The denominator 1000 can be expressed in the power of 2 and 5 as:

$1000=2^3\times 5^3$  

So, the given rational number is a terminating rational number.