Which of the following substances dissociates into ions when placed in water?

• A. CO_2
• B. C_6H_{12}O_6 (glucose)
• C. NaCl
• D. CH_3OH (methanol)

Answer: (C)

Verified step by step guidance

1. Understand the concept of dissociation in water: When a substance dissociates in water, it separates into its constituent ions, which can conduct electricity, making the solution an electrolyte.
2. Identify the nature of each substance: CO_2 is a molecular compound that dissolves in water but does not dissociate into ions; it forms a weak acid (carbonic acid) instead.
3. C_6H_{12}O_6 (glucose) is a covalent molecular compound that dissolves in water but remains as whole molecules without producing ions.
4. NaCl is an ionic compound composed of Na^+ and Cl^- ions; when placed in water, it dissociates completely into these ions, making the solution conductive.
5. CH_3OH (methanol) is a covalent molecular compound that dissolves in water but does not dissociate into ions; it remains as neutral molecules.