Problem: Given the background: Of the 94 naturally occurring elements, those with atomic numbers 1 through 82 each have at least one stable isotope (except for technetium, element 43 and promethium, element 61, which have no stable isotopes). Isotopes considered stable are those for which no radioactive decay has yet been observed. Elements with atomic numbers 83 through 94 are unstable to the point that radioactive decay of all isotopes can be detected. Some of these elements, notably bismuth (atomic number 83), thorium (atomic number 90), and uranium (atomic number 92), have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy metals before the formation of our Solar System. At over 1.91019 years, over a billion times longer than the current estimated age of the universe, bismuth-209 (atomic number 83) has the longest known alpha decay half-life of any naturally occurring element, and is almost always considered on par with the 80 stable elements. The very heaviest elements (those beyond plutonium, element 94) undergo radioactive decay with half-lives so short that they are not found in nature and must be synthesized. and the situation: David was studying for his chemistry exam. To understand the elements of the periodic table better he categorized them into three groups, cat A, cat B, and cat C. In cat A he placed all the elements with atomic numbers lower than 83. In cat B he put the elements with atomic numbers from 83 to 94. Finally, in cat C he placed the elements with atomic numbers over 94. He found it easier to see their differences after he categorized them. Answer the following question: Would cat A more likely or less likely show radioactive decay than cat B?

A: less likely

Problem: Given the background: Collision theory tells us that molecules need to collide in order for a reaction to take place. All else being equal, anything that increases the frequency of collisions would also increase the rate of reaction. One way to do this is to increase the concentrations of one or more of the reactants. Using a real world example, a busy freeway will experience much more frequent car collisions than a fairly empty neighborhood street. Similarly, forcing more randomly moving molecules into the same amount of space will cause an increased number of collisions over a given length of time, providing the reactants with more opportunities to transform into products. and the situation: Jordan and Elizabeth are performing a chemistry experiment for the science fair. Jordan uses a high concentration of the reactants when starting his reactions. Elizabeth uses a low concentration of the reactants when she starts her reactions. Answer the following question: Who will have reactions with more frequent collisions between the reactant molecules?

A: Jordan

Problem: Given the background: Arbuscular mycorrhizal fungi vary across many environmental gradients. Their tolerance to freezing and drying is known to shift between AM fungal taxa. AM fungi become less prevalent and diverse at higher soil nutrient and moisture concentrations, presumably because both plants allocate less carbon to AM fungi and AM fungi reallocate their resources to intraradical hyphae in these environmental conditions. Over the long term, these environmental conditions can even create local adaptation between plant hosts, AM fungi and the local soil nutrient concentrations. and the situation: Greg and Paul were two neighbors. They were both into mycology. Greg researched AM fungi, while Paul studied other types of mycorrhizal fungi. Answer the following question: Which researcher learned more about plants allocating less carbon to AM fungi?

A: Greg

Problem: Given the background: We all enjoy a cool dip in a swimming pool on a hot day, but we may not realize the work needed to keep that water safe and healthy. The ideal pH for a swimming pool is around 7.2. The pH will change as a result of many factors. Adjustment can be accomplished with different chemicals depending on the tested pH. High pH can be lowered with liquid HCl (unsafe material) or sodium bisulfate. The bisulfate anion is a weak acid and can dissociate partially in solution. To increase pH, use sodium carbonate. The carbonate anion forms an equilibrium with protons that results in some formation of carbon dioxide. and the situation: Tom and John are both pool owners. Tom prefers to use sodium bisulfate in his pool because he enjoys the smell. John, however, prefers using sodium carbonate in his pool because he believes it helps keep pests away. Answer the following question: Whose pool will have lower levels of carbon dioxide?

A:
Tom