The compound which forms acetaldehyde when heated with dilute $NaOH$ is

$A$ halogen compound $X$ $(C_4 H_9 Br)$ on hydrolysis gives an alcohol $Y$. The alcohol $Y$ undergoes dehydration with $20 \% H_3 PO_4$ at $358 \ K$. What is $X$?

Which of the following are correct statements about $C_2H_5Br$?

Which of the following is the correct decreasing order of the boiling point of the given compounds?

$2-$chloro$-2-$methylpentane on reaction with sodium methoxide in methanol yields:
$(1)\ C_2H_5-CH_2-C(CH_3)_2-OCH_3$
$(2)\ C_2H_5-CH_2-C(CH_3)=CH_2$
$(3)\ C_2H_5-CH=C(CH_3)_2$

$50\%$ of the reagent is used for dehydrohalogenation of $6.45 \ g$ $CH_3CH_2Cl$. What will be the weight of the main product obtained (in $g$)? [At. mass of $H$,$C$,and $Cl$ are $1$,$12$,and $35.5 \ g \ mol^{-1}$ respectively]