Correct option:(3)Gamma rays

Solution:

• Several kinds of radiation like gamma rays, X-rays, UV-rays cause mutation.
• These are physical mutagens.
• Such induced mutation in plants is done to develop improved varieties.
• The first natural cytokinin was isolated from unripe maize grain known as zeatin.
• The cytokinin that was obtained from degraded product of autoclaved herring sperm DNA was kinetin (N6-furfuryl aminopurine).
• Infrared rays cause heating effect.