An alkene,on ozonolysis,gives formaldehyde and acetaldehyde. The alkene is:

What is the major product obtained when $1$-butanol is heated with concentrated $H_2SO_4$?

In the reaction with $HCl$,an alkene reacts in accordance with Markovnikov's rule to give the product $1-$chloro$-1-$methylcyclohexane. The possible alkene is:

$A \xleftarrow[\Delta]{Cu} CH_3CH_2OH \xrightarrow[\Delta]{Al_2O_3} B$. $A$ and $B$ respectively are

Product $(A)$ will be

In the reaction of hydrogen bromide with an alkene (in the absence of peroxides),the first step of the reaction is the ................. to the alkene.