Answer
$y= 2^{-x} -1$, or (C)
Work Step by Step
Transformation 1: for any function $f(x)$, a reflection across the y-axis turns that function into $f(-x)$. In this case of this function, it becomes $y=2^{-x}$.
Transformation 2: to move up or down by k units, the entire function needs to be added or subtracted by k. In this case, 1 needs to be subtracted, so the result is $y = 2^{-x}-1$
