Bronze is best known as an alloy of copper and tin, but copper alloyed with aluminum, arsenic, manganese, phosphorous, silicon, etc., can also referred to as bronzes.
Yes, it is, see this 2010 paper Eating artificially ripened fruits is harmful. Calcium carbide is extremely hazardous to the human body as it contains traces of arsenic and phosphorus. It is banned in many countries of the world, but it is freely used in India, Pakistan, Bangladesh, Nepal and other countries. Thus we are at risk of short-term and long-term health effects simply by eating fruits that are induced to ripen. Calcium carbide CaC2 is used to easily generate low levels of ethylene gas which can hasten the (outside at least) ripening of fruits like bananas, mangoes etc.
3) In a paper bag: takes about 12-24 hours to ripen. Place bananas in a brown paper bag and close loosely. Ethylene will build up and circulate within the bag, speeding up the ripening process. Check at certain intervals in order to take them out at your desired ripeness.