Alkenes and alkynes burn with a .......... . flame.

Explanation

**Step-by-Step Solution:**

1. **Understanding Alkenes and Alkynes:**
- Alkenes and alkynes are types of unsaturated hydrocarbons. Alkenes contain at least one carbon-carbon double bond (C=C), while alkynes contain at least one carbon-carbon triple bond (C≡C).

2. **Combustion of Hydrocarbons:**
- When hydrocarbons burn in the presence of oxygen, they undergo combustion. This process can be complete or incomplete depending on the amount of oxygen available.

...