Why is 1 position in naphthalene more reactive in electrophilic substitution

The most efficient stabilization of the intermediate carbocation produced by electrophilic attack on naphthalene comes from those resonance forms which retain one fully benzenoid ring. In the case of 1-substitution, two such structures can be drawn (A, B). For 2-substitution there is only one structure (F). The intermediate from attack at the 1-position is more stable and therefore the 1-substituted product is favoured in the reactions of electropholic substitution of naphthalene.