Pick the correct statement. I. Borax is white crystalline solid containing [ B ₄ O ₅( OH )₄ ]²⁻ units. II. Aqueous solution of borax is acidic in nature. III. Cobalt gives blue colour in borax bead test.

Step-by-step solution

I. Structural formula of borax ( Na ₂ ~B ₄ O ₇ 10 H ₂ O ) is Na ₂ [ ~B ₄ O ₅( OH )₄ ] 8 H ₂ O correct statement. II. Aqueous solution of borax is basic in nature, because borax in water dissociates into H ₃ BO ₃ (weak acid) and NaOH (strong base). Na ₂ ~B ₄ O ₇+7 H ₂ O 4 H ₃ BO ₃+2 NaOH Incorrect statement. III. Cobalt (Co) gives blue colour of cobalt metaborate [ Co ( BO ₂ )₂ ] in borax bead ( NaBO ₂+ B ₂ O ₃ ) test Correct statement. So, the correct statements are (I) and (III).