Problem: Two brothers worked out a few times per week at the same gym. Tim got athlete's food from the gym, but Dan didn't. Which brother picked up the second most common skin disease in the US? Hint: Other pathogens spread when they get on objects or surfaces. A fungus may spread in this way. For example, you can pick up the fungus that causes athlete's foot by wearing shoes that an infected person has worn. You can also pick up this fungus from the floor of a public shower or other damp areas. After acne, athlete's foot is the most common skin disease in the United States. Therefore, the chance of coming in contact with the fungus in one of these ways is fairly high.

A: Tim

Problem: Lawmakers were debating the pros and cons of Keystone XL Pipeline. One group of lawmakers proposed that the pipeline be constructed. They put their proposal in proposal A. The rival group of lawmakers proposed that the pipeline should not be build. They put their proposal in proposal B. Lawmakers would now have to choose one of the proposals. Which proposal might contaminate the aquifer, proposal A or proposal B? Hint: The Keystone XL Pipeline would transport oil from the oil sands in Alberta, Canada. The oil would travel into the United States. In the U.S. it would be refined. The pipeline is controversial. A leak could cause damage to wildlife habitat. A leak could also release enough oil to contaminate the Ogallala Aquifer. The Aquifer is crucial to agriculture and urban development in the Midwestern U.S. When burned, the fuel from the oil sands would increase pollutants. Greenhouse gases into the atmosphere would increase. The future of the pipeline is currently on hold.

A: proposal A

Problem: John was interested in climate change issues. To that end, he studied two imaginary situations, case A and case B. In case A, there would not be excessive greenhouse gases in the atmosphere. On the contrary, in case B, the amount of greenhouse gases in the atmosphere would increase dramatically. John realized that the amount of greenhouse gases in the atmosphere has many practical implications. In which case global temperature would be lower, case A or case B? Hint: Greenhouse Effect: The solar energy reaching the surface of the Earth is concentrated in short wavelengths, which can easily penetrate the greenhouse gases, such as carbon dioxide and methane. The Earth, however, is cooler than the sun and it radiates its heat in the form of energy in the far infrared range. These longer wavelengths are partially absorbed by the greenhouse gases and some of the solar heat is returned to Earth. At a certain temperature these processes are in equilibrium and the surface temperature of the Earth is stable. However, if more greenhouse gases are put in the atmosphere the amount of trapped terrestrial radiation increases, leading to an increase in global temperature.

A: case A

Problem: Students in a chemistry class are performing experiments using two different compounds. The first compound, compound A, has a high number of hydrogen bonds between molecules of the compound. The second compound, compound B, has a low number of hydrogen bonds between the molecules of the compound. Aside from this difference, the molecular structure between the two compounds is similar. Which compound will require less energy to undergo state changes? Hint: Changes of state from solid to liquid and from liquid to gas occur when matter gains energy. The energy allows individual molecules to separate and move apart from one another. It takes more energy to bring about these changes of state for polar molecules. Although hydrogen bonds are weak, they add to the energy needed for molecules to move apart from one another, so it takes higher temperatures for these changes of state to occur in polar compounds. This explains why polar compounds have relatively high melting and boiling points. The Table below compares melting and boiling points for some polar and nonpolar covalent compounds.

A:
compound B