23. Greenhouse effect is caused by A.Nitrogen B.Carbon dioxide C.Carbon monoxide D.Nitrogen dioxide
Answer: Option D Solution: Brown stains in vessels and clothes generally indicate the presence of high quantities of iron. It causes reddish-brown staining of laundry, porcelain, dishes, utensils and even glassware. Manganese acts in a similar way but causes a brownish-black stain. Soaps and detergents do not remove these stains.
