What by-product is formed in the process of making phenol from cumene?

Describe the methods and processes for the production of phenol.

Cumene on air oxidation in the presence of cobalt naphthenate forms:

The major product formed in the following reaction sequence is:

Identify the substrate $X$ in the following reaction. $X + O_2 \text{ (air)}$ $\xrightarrow[\text{ii) dil } HCl, \Delta]{\text{i) Co-naphthenate, } 423 \ K} \text{Phenol} + \text{Acetone}$

$X, Y$ and $Z$ in the following reaction sequence are