Pick the correct statement. I. Borax is white crystalline solid containing $\left[\mathrm{B}_4 \mathrm{O}_5(\mathrm{OH})_4\right]^{2-}$ units. II. Aqueous solution of borax is acidic in nature. III. Cobalt gives blue colour in borax bead test.

I. Structural formula of borax $\left(\mathrm{Na}_2 \mathrm{~B}_4 \mathrm{O}_7 \cdot 10 \mathrm{H}_2 \mathrm{O}\right)$ is $\mathrm{Na}_2\left[\mathrm{~B}_4 \mathrm{O}_5(\mathrm{OH})_4\right] \cdot 8 \mathrm{H}_2 \mathrm{O} \Rightarrow$ correct statement. II. Aqueous solution of borax is basic in nature, because borax in water dissociates into $\mathrm{H}_3 \mathrm{BO}_3$ (weak acid) and $\mathrm{NaOH}$ (strong base). $\mathrm{Na}_2 \mathrm{~B}_4 \mathrm{O}_7+7 \mathrm{H}_2 \mathrm{O} \longrightarrow 4 \mathrm{H}_3 \mathrm{BO}_3+2 \mathrm{NaOH} \Rightarrow$ Incorrect statement. III. Cobalt (Co) gives blue colour of cobalt metaborate $\left[\mathrm{Co}\left(\mathrm{BO}_2\right)_2\right]$ in borax bead $\left(\mathrm{NaBO}_2+\mathrm{B}_2 \mathrm{O}_3\right)$ test $\Rightarrow$ Correct statement. So, the correct statements are (I) and (III).