Matter is anything that has mass and volume
Ultraviolet Rays ( UV rays) can harm humans because they can cause sunburn, and skin cance if you stay out in the sun for too long.
Answer:
Kr has one more electron than br and so, the nuclear charge increase, which means the nuclear attraction between the nucleus and outer most electron will increase and so will be harder to remove the electron from Kr than Br, so Kr has higher 1st ionisation.
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