No, it is not safe to put a grape in the microwave. When grapes are microwaved, they can potentially spark and create small plasma fires. This phenomenon is known as "microwave grape plasma." The sparks occur due to the grape's size and shape, which allows for an accumulation of energy in certain spots, leading to a discharge of electricity.
It is essential to exercise caution when using a microwave to avoid any potential hazards. Always refer to the microwave's user manual for guidelines on what items can be safely microwaved. If you are uncertain about whether a particular food or object is microwave-safe, it's best to avoid microwaving it altogether to prevent accidents or damage to the appliance.