How to write an If...Then...Because hypothesis statement

Make a hypothesis about which part of the light spectrum causes the most plant growth and which part of the light spectrum causes the least plant growth.

If plants are exposed to red light, then they will experience the most growth because red light is the most beneficial wavelength for photosynthesis. If plants are exposed to green light, then they will experience the least growth because green light is the least effective for driving the process of photosynthesis.