After Shabbos, my wife found a shekel coin under a pillow of our rocking chair. Did the chair become a bosis of mukzah because of the coin? May I ask your sources be in English, please
The chair is not a bosis and it may be moved.
There are a number of conditions in order for an object to become a bosis. The first one is that the item has to be placed there with the intention that it will stay there for Shabbos. In our case the coin was forgotten and got lost in the chair. therefore the chair will not be rendered a bosis. Another reason it will not become a bosis is because the shekel coin is insignificant to the value of the rocking chair, and a muktza that is insignificant to the vlue of the item that is supporting it will not become a bosis.
Regarding the sources, there are times that they have to be written in Hebrew, and times that I can write them in English.
Shabbos 142b, Shulchan Aruch O:CH 309-4, Mishna Berura 309- 18, 310-31..