The formation Alkenes by the dehydration of alcohols (using concentrated H2SO4) the hydrogen atom will be separate (to remove as water) from the adjacent carbon atom correlated to the less number of hydrogen atoms.
Example: In the dehydration of Butane - 2Ol
2Butane is produced
CH3-CH=CH-CH3+H2Oàconcentrated H2SO4àCh3-CH2-CH-CH3
But2-ene