Q: When a stream flows from a hard to soft rock area, what is often formed? Read this paragraph and choose the correct option from the provided answers: Mountain streams may erode waterfalls. As shown in Figure below , a waterfall forms where a stream flows from an area of harder to softer rock. The water erodes the softer rock faster than the harder rock. This causes the stream bed to drop down, like a step, creating a waterfall. As erosion continues, the waterfall gradually moves upstream. Choices: - a lake - a river - a riverbank - a waterfall A:
a waterfall

Q: What happens if a molecule forms strong bonds to the catalyst? Read this paragraph and choose the correct option from the provided answers: In catalysis, if a molecule forms strong bonds to the catalyst, then the catalyst may become poisoned. Experiments on various catalysts showed the following results: a. Fe, Ru, and Os form weak bonds with N2; however, O2, alkynes, alkenes, CO, H2, and CO2 interact more strongly. CO2 and H2 form weak bonds with a Co or Ni surface. Rh, Pd, Ir, and Pt form weak bonds with H2 but do not bond with CO2. Cu, Ag, and Au form weak bonds with CO and ethylene. Explain why Fe was chosen as a catalyst to convert nitrogen and hydrogen to ammonia. Why is Fe more suitable than Ru or Os? f. Because alkenes generally interact more strongly with metal surfaces than does H 2, what catalyst would you choose for hydrogenation of an alkene such as ethylene? g. Although platinum is used in catalytic converters for automobile exhaust, it was not found to be a particularly effective catalyst for the reaction of H2 with a mixture of carbon monoxide and carbon dioxide to produce methane. Why? h. If you were interested in developing a catalyst to reversibly bind ethylene, which of the catalysts listed here would you choose? 14. Nonstoichiometric metal oxides can be effective catalysts for oxidationreduction reactions. One such catalyst is Ni1xO, found to be effective for converting CO to CO2when oxygen is present. Why is it so effective? 15. The chemical reactions in an organism can be controlled by regulating the activity of certain enzymes. Efficient regulation results in an enzyme being active only when it is needed. For example, if a cell needed. Choices: - molecules gets poisoned - surface gets poisoned - membrane gets poisoned - catalyst gets poisoned A:
catalyst gets poisoned

Q: What is considered the center of the solar system? Read this paragraph and choose the correct option from the provided answers: Today we know that we have eight planets, five dwarf planets, over 165 moons, and many, many asteroids and other small objects in our solar system. We also know that the Sun is not the center of the universe. But it is the center of the solar system. Choices: - nebulla - earth - heat - sun A:
sun

Q: When warm air rises up to the tropopause, where does it flow? Read this paragraph and choose the correct option from the provided answers: Earth is hottest at the equator and gets cooler toward the poles. The differences in heating create huge convection currents in the troposphere. At the equator, for example, warm air rises up to the tropopause. It can't rise any higher, so it flows north or south. Choices: - east or north - west or south - east or west - north or south A:
north or south