Cant get these wrong. asexual n sexual reproduction
budding in yeast sexual or asexual reproduction?
mushrooms producing spores sexual or asexual reproduction?
creation of an egg sexual or asexual reproduction?
production of seeds sexual or asexual reproduction?
creation of fruit sexual or asexual reproduction?
stem cuttings of plants sexual or asexual reproduction?

Explanation:

After the Becquerel came to know the discovery of X-ray by Roentgen  Becquerel began looking for a connection between the phosphorescence  and the newly discovered X-rays. His thought was that phosphorescent uranium salts might absorb sunlight and reemit it as x rays.

To experiment this  he exposed a sample of uranium to sunlight, and then was pleased to discover that the uranium continued to emit energy even after it was taken out of the light. However, after several straight days of cloudy skies over his laboratory, Becquerel was shocked to discover that the energy kept coming from the uranium,  

He reported that the uranium salts emitted radiation without any stimulation from sunlight.  He did further tests to confirm that sunlight was indeed unnecessary, that the uranium salts emitted the radiation on their own.

Initially he thought the effect was due to particularly long-lasting phosphorescence, but he soon discovered that non-phosphorescent uranium compounds exhibited the same effect. After that he announced that the element uranium was indeed what was emitting the radiation.  

At first he also believed his rays were similar to x-rays, but his further experiments showed that unlike x-rays, which are neutral, his rays could be deflected by electric or magnetic fields which was against his expectations. Finally “Radioactivity” term was given to describe this new phenomenon.

This story of becquerel is well known example of accidental discovery.