ANS:C - crystallise out at low temperature.

Waxes present in petroleum products typically crystallize out at low temperatures. Here's why:

1. Nature of Waxes: Waxes are high-molecular-weight hydrocarbons that solidify at relatively high temperatures compared to other components in petroleum products. They are composed mainly of long-chain saturated hydrocarbons.
2. Crystallization: When the temperature of a petroleum product containing waxes decreases, these waxes tend to crystallize out of the liquid phase. This phenomenon is due to their molecular structure and the intermolecular forces that promote solidification under specific temperature conditions.
3. Separation and Solubility: Waxes are generally not soluble in the liquid phase of petroleum products at typical operating temperatures. While they can be separated by processes like solvent extraction or filtration, distillation is typically not effective for separating waxes due to their high boiling points and tendency to solidify rather than vaporize.
4. Effect on Viscosity: The presence of waxes in petroleum products, especially at higher temperatures, can contribute to increased viscosity. However, at lower temperatures, their crystallization can lead to a decrease in fluidity and flow characteristics, affecting product handling and performance.