Identify the correct statements from the following : I. Ga_2 O_3 is...

(I) $\mathrm{Ga}_2 \mathrm{O}_3$ is an amphoteric oxide is the correct statement as it reacts with acid and base both, as shown below : Reaction with an acid \mathrm{Ga}}_{2} \mathrm{O}}_{3}+6\mathrm{HCl} \longrightarrow$2$\mathrm{GaCl}}_{3}+3 \mathrm{H}}_{2} $\mathrm{O}$Reaction with a base \mathrm{Ga}}_{2} \mathrm{O}}_{3}+2\mathrm{NaOH} \longrightarrow$2$\mathrm{NaGaO}}_{2}+ \mathrm{H}}_{2} $\mathrm{O} ($II) The dimer of aluminium chloride has three $\mathrm{Al}-\mathrm{Cl}-\mathrm{Al}$ bridge bond is not the correct statement as structure of $\mathrm{Al}_2 \mathrm{Cl}_6$ is as follows:
(III) Boron is very hard refractory solid of high melting temperature is the correct statement as its melting point is $2349 \mathrm{~K}$ and is used as refractory solid. Hence, option (b) is the correct answer.