In the reaction $\left(\mathrm{X}\right)$ and $\left(\mathrm{Y}\right)$ are respectively.

The correct sequence of reagents for the following conversion will be

The addition of $\mathrm{HBr}$ to $1$-butene gives a mixture of products $\mathrm{x}, \mathrm{y}$ and $\mathrm{z}$

The mixture consists of

In the compound, 

$\underset{\left(\mathrm{I}\right)}{{\mathrm{CH}}_2}=\underset{\left(\mathrm{II}\right)}{\mathrm{CH}}-\mathrm{C}\underset{\left(\mathrm{III}\right)}{\equiv \mathrm{CH}}$

The most acidic hydrogen atom is