To find the function \( g(x) \) that corresponds to reflecting the function \( f(x) = -2x + 1 \) across the x-axis, we need to change the sign of the entire function. This means that we must multiply the function \( f(x) \) by \(-1\).
Starting with:
\[ f(x) = -2x + 1 \]
Reflecting this across the x-axis gives us:
\[ g(x) = -f(x) = -(-2x + 1) = 2x - 1 \]
So the function \( g(x) \) after reflection is:
\[ g(x) = 2x - 1 \]
From the provided responses, the correct choice is:
\[ g(x) = 2x - 1 \]
Or written in another format:
\[ g \left( x \right) = 2 x - 1 \]