The relation 'less than' on the set of natural numbers is 

$\begin{array}{l}\text{ As }x<y,y<z\Rightarrow x<z\mathrm{\forall }x,y,z\in N\\ \therefore xRy,yRz\Rightarrow xRz,\therefore \text{ Relation is transitive }\\ \therefore x<y\text{ does not give }y<x,\end{array}$

$\therefore \text{ Relation is not symmetric }$

$\text{ As }x<x\text{ does not hold, hence relation is not reflective }$