What is the number of $\sigma$ and $\pi$ bonds in $Pent-1-en-4-yne$?

What is the stereochemistry of the product formed in the following reaction?

Which of the following compounds was the starting material for the oxidation shown below?

What are $X$ and $Y$ respectively in the following sets of reactions?
$I. \ CH_3CH_2CH_2OH \xrightarrow{PBr_3} X$
$II. \ CH_3CH=CH_2 \xrightarrow{HBr, (C_6H_5COO)_2} Y \text{ (major)}$

In the given sequence of reactions,identify $P, Q, R$ and $S$ respectively.
$CH_2=CH_2 + Br_2$ $\xrightarrow{P} CH_2(Br)-CH_2(Br)$ $\xrightarrow{Q} CH_2=CH-Br$ $\xrightarrow{R} CH \equiv CH$ $\xrightarrow{S} C_6H_6$

Arrange benzene,$n-$hexane and ethyne in decreasing order of acidic behaviour. Also give reason for this behaviour.