(b)
Since, $x,\ y,\ \mathcal{z}$ are in GP.
$\therefore\ \ y^{2} = x\mathcal{z}$
$\Rightarrow \ 2\log{y = \log{x + \log\mathcal{z}}}$
$\Rightarrow \ \ 2(\log{y + 1) = (1 + \log{x) + (1 + \log\mathcal{z)}}}$
$\Rightarrow \ \ 1 + \log{x,\ 1 + \log{y,\ 1 + \log\mathcal{z}\ }}$ are in AP
$\Rightarrow \ \frac{1}{1 + \log x},\frac{1}{1 + \log y},\frac{1}{1 + \log\mathcal{z}}$ are in HP.