(N/A) $\alpha, \beta$-Hydrogen: The carbon atom to which the halogen is attached is called the $\alpha$-carbon atom,and the carbon atoms adjacent to this $\alpha$-carbon are called $\beta$-carbon atoms. The halogen attached to the $\alpha$-carbon is the $\alpha$-halogen,and the $H$ atoms attached to the $\beta$-carbon are called $\beta$-hydrogen atoms.
$(b)$ Dehydrohalogenation or $\beta$-elimination reaction: When a haloalkane containing $\beta$-hydrogen is heated with an alcoholic solution of potassium hydroxide $(KOH)$,a hydrogen atom from the $\beta$-carbon and a halogen atom $(X)$ from the $\alpha$-carbon are eliminated to form an alkene as the product along with hydrogen halide $(HX)$. This reaction is generally called a $\beta$-elimination or dehydrohalogenation reaction.
$(c)$ Saytzeff rule and $\beta$-elimination: In $1875$,the Russian chemist Alexander Saytzeff proposed a rule to determine the major alkene product formed from haloalkanes containing more than one type of $\beta$-hydrogen.