Final Answer:
Adding formaldehyde decreases the boiling point of water (option B). The primary effect is colligative lowering of boiling point.
Step-by-step explanation:
When a non-volatile solute like formaldehyde is added to water, it disrupts the intermolecular forces between water molecules, making it easier for them to escape into the vapor phase and lowering the boiling point. This phenomenon is known as colligative lowering of boiling point. The extent of the decrease depends on the concentration of the solute but not its identity.
Here's a simple analogy: Imagine water molecules as tightly packed puzzle pieces. Adding formaldehyde is like throwing in a few extra pieces that don't fit perfectly, disrupting the overall structure and making it easier for the pieces (water molecules) to come loose and "boil" into the vapor phase.
Therefore, options A, C, and D are incorrect:
Option A (Increased boiling point): This is the opposite of what happens when a non-volatile solute is added.
Option C (No effect on boiling point): While some solutes may have minimal impact on boiling point, formaldehyde is not one of them.
Option D (Formation of azeotropes): Azeotropes are constant boiling point mixtures where the liquid and vapor phases have the same composition. While formaldehyde can form azeotropes with water at specific concentrations, this is not the primary effect of adding it to water.
Colligative properties like boiling point depression depend on the concentration of the solute particles, not their identity. So, the specific chemical properties of formaldehyde play a less significant role in this context compared to the general principle of disrupting intermolecular forces.
Option B is answer.