Question

why primary alcohol is more reactive than secondary alcohol?

Answer 1

alcohol contain drowsiness
in primary alcohol this content is more
hence it is more reactive than secondary alcohol

Answer 2

it will become more stable there for it is thermodynamycally favorite. so the reactivity is heigher than primary or secondary alcohol. Tertiary alcohols are more reactive because the increased number of alkyl groups increases effect. So, the charge density on carbon atom increases and hence around oxygen atom.