In the set of straight lines in a plane, for the relation 'perpendicular' check whether it is reflexive, symmetric and transitive.

Explanation

To determine whether the relation 'perpendicular' among straight lines in a plane is reflexive, symmetric, and transitive, we will analyze each property step by step.

### Step 1: Check for Reflexivity
A relation is reflexive if every element is related to itself. In this case, we need to check if a line is perpendicular to itself.

- **Analysis**: No line can be perpendicular to itself. For example, if we take line AB, it cannot be perpendicular to line AB because perpendicular lines intersect at a right angle, which is not possible for the same line.

- **Conclusion**: The relation 'perpendicular' is **not reflexive**.
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