Benzene diazonium chloride on reaction with phenol in weakly basic medium gives:

When phenol and benzene diazonium chloride combine in a slightly basic solution, p-Hydroxyazobenzene, an orange colour, is produced.

In a basic media, benzene diazonium chloride reacts with phenol to produce p-Hydroxy azobenzene. A prime illustration of the coupling reaction is this.

Hence, the option B is correct.