When a point \((x, y)\) is reflected horizontally across the y-axis, the x-coordinate changes its sign, while the y-coordinate remains the same.
For the point \((2, -4)\):
- The x-coordinate \(2\) becomes \(-2\).
- The y-coordinate \(-4\) remains \(-4\).
Thus, after the reflection, the point \((2, -4)\) becomes \((-2, -4)\).
So the correct response is: In the horizontal reflection, the point (2,−4) becomes (−2,−4).