Final answer:
The chemical formula for cobalt (II) hydroxide is Co(OH)₂, which is answer option A.
Step-by-step explanation:
The chemical formula of cobalt (II) hydroxide is Co(OH)₂. This compound consists of one cobalt ion with a +2 charge and two hydroxide ions, each with a -1 charge.
The parentheses with the subscript 2 indicate that there are two hydroxide ions for every one cobalt ion, balancing the charges to zero for a neutral compound.
Therefore, the correct answer to the student's question is A) Co(OH)₂.