What is a substance that is made up of only atoms of one type?

If 22.5 of nitrogen at 748 mm hg are compressed to 725 mm hg at constant temperature. what is the new volume?

Liquid from a brewery fermentation contains 10% ethanol and 90% water. part of the fermentation product (50,000 kg/h) is pumped to a distillation column on the factory site. under current operating conditions, a distillate of 45% ethanol and 55% water is produced from the top of the column at a rate of one-tenth that of the feed. what is the composition of the waste "bottoms" from the still?

In medium-sized stars such as the sun, nuclear fusion almost always means the fusing of nuclei to form , but larger stars can produce elements as heavy as