We need to compute the derivative of the given expression. The limit as \( n \to 1 \) of \( \frac{x^n - 1}{n+1} \) simplifies to \( \frac{x - 1}{2} \). Differentiating this with respect to \( x \), we get:
\[
\frac{d}{dx} \left( \frac{x - 1}{2} \right) = \frac{1}{2}.
\]
Thus, the correct answer is option (B) \( \frac{1}{2} \).