Question

perpendicular lines have: equal length opposite & reciprocal slope nothing in common equal slope

Explanation:

Perpendicular lines in a coordinate - plane have slopes that are negative reciprocals (opposite and reciprocal) of each other. For example, if one line has a slope of $m_1$, the slope of a line perpendicular to it is $m_2=-\frac{1}{m_1}$. Their lengths are not related, and equal - slope lines are parallel.

Answer:

B. opposite & reciprocal slope