How much of earth's atmosphere is made up of nitrogen and oxygen?
a. between 25 and 75 percent
b. close to 99 percent
c. less than 1 percent
d. 100 percent

If a 60-g object has a volume of 30 cm3, what is its density? 2 g/cm3 0.5 cm3/g 1800 g * cm3 none of the above

Aluminum reacts with chlorine gas to form aluminum chloride via the following reaction: 2al(s)+3cl2(g)→2alcl3(s) what is the maximum mass of aluminum chloride that can be formed when reacting 32.0 g of aluminum with 37.0 g of chlorine? express your answer to three significant figures and include the appropriate units.

Several kinds of bears are found on earth. most bears are brown or black, but one type of bear, the polar bear, is white. what process led to this difference in fur color? explain your answer.