Elimination reaction (especially `beta` - elimination) are as common as the nucleophilic substitution reaction in case of alkyl halides. Specify the reagents used in both cases.

Explanation

Both elimination reactions (particularly `beta`-elimination reactions) and nucleophilic substitution reactions occur simultaneously. However, by a proper choice of reagents and reaction conditions, we can make one reaction to predominate over the other. Usually strong and bulkier bases and high temperature favour elimination reactions whereas weaker and smaller bases and lower temperature favour substitution reactions. For example, ethyl bromide on heating with alcoholic KOH (which contains the stronger base `C_(2)H_(5)O^(-)` ion) at about 473-523K undergoes elimination to give ethene while with aqueous KOH at about 373K it gives ethanol.
`underset("Ethanol")(CH_(3)CH_(2)OH) underset("373K (Substitution)")overset(KOH(aq))to underset("Ethyl bromide")(CH_(3)CH_(2)Br) underset("473-523K (Elimination)")overset(KOH(alc))to underset("Ethene")(CH_(2)=CH_(2))`