Choice A is the correct answer. Perpendicular lines have negative reciprocal slopes.

1. Original Slope: $m = -\frac{1}{2}$.
2. Negative Reciprocal: Flip the fraction ($2/1$) and change the sign ($+$).
3. Result: $2$.

💡 Strategic Tip: The product of perpendicular slopes is -1. $(-1/2) \times 2 = -1$.

Choice B is incorrect because it only flips the fraction. Choice C is incorrect because it only changes the sign. Choice D is incorrect because it is the same slope (parallel).