Let R be the relation over the set of straight lines of a plane ,such that l₁Rl₂ $\iff$l₁ $\perp$ l₂   Then R is 

l₁R l₁$\Rightarrow$    l₁ is not perpendicular to   l₁

R is not reflexive 

 l₁ R l ₂ $\Rightarrow$ l₁$\perp$l ₂

$\Rightarrow$ l₂$\perp$l ₁

$\Rightarrow$ l₂ R l ₁ $\therefore$ Hence R is symmetric

 $l_{1}R{l}_{2 }and l_{2}R l_3 \Rightarrow l_1\cancel{R}{l}_3$

$\therefore$R is not transitive