When dissolved in a dilute aqueous solution, formaldehyde predominantly exists as:

Step-by-step solution

Formaldehyde ( HCHO ) reacts with water in a dilute aqueous solution to undergo hydration. The reaction is: HCHO + H ₂ O CH ₂( OH )₂ The product CH ₂( OH )₂ is a gem-diol known as methylene glycol. Due to the absence of steric hindrance and the high electrophilicity of the carbonyl carbon in formaldehyde, the equilibrium lies almost completely to the right. Thus, in a dilute aqueous solution, formaldehyde predominantly exists as methylene glycol (nearly 99.9 % ).