Correct option: B.$f$ is differentiable for all $x$, except at $x=n \pi, n=\pm 1, \pm 2, \pm 3, \ldots$
b
(b)
We have, $f(x)=x|\sin x|, x \in R$
$f(x)=\left\{\begin{array}{ll} x \sin x, & x \in(2 n \pi,(2 n+1) \pi) \\ -x \sin x, & x \in((2 n+1) \pi, 2 n \pi) \end{array}\right.$
$f^{\prime}(n \pi)=\lim _{x \rightarrow n \pi} \frac{f(x)-f(n \pi)}{x-n \pi}$
$=\lim _{x \rightarrow n \pi} \frac{x \sin x \mid}{x-n \pi}$
Clearly, $f(x)$ is differentiable for all $x$ except $x=n \pi, n=\pm 1, \pm 2, \pm 3, \ldots$