Given the background: If a solution has a higher concentration of hydronium ions than pure water, it has a pH lower than 7. A solution with a pH lower than 7 is called an acid . As the hydronium ion concentration increases, the pH value decreases. Therefore, the more acidic a solution is, the lower its pH value is. Did you ever taste vinegar? Like other acids, it tastes sour. Stronger acids can be harmful to organisms. For example, stomach acid would eat through the stomach if it were not lined with a layer of mucus. Strong acids can also damage materials, even hard materials such as glass. and the situation: Alexiev and Sabrina were enthusiastic chemistry students completing the first experiment of their new course. They both started the experiment with pure water, and had to perform different experimental protocols to make changes to the water. At the end of the experiment, both of them measured the concentration of hydronium ions present in their reaction mixtures. Alexiev had a high concentration of hydronium ions present, while Sabrina had a low concentration present in her mixture. Answer the following question: Which person's mixture, Alexiev's or Sabrina's, has a higher pH value at the end?
Ans: Sabrina's

Given the background: About 10% of sedimentary rocks are limestones. The solubility of limestone in water and weak acid solutions leads to karst landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock. and the situation: Peter visited two mountain ranges last summer. The Ozarks in Missouri, and the more massive and younger Colorado Rockies. He loved both ranges, but liked the caves systems and blue holes in the Ozarks a bit more. Answer the following question: Which mountains have a larger percent of sedimentary rock?
Ans: the Ozarks

Given the background: Old age begins in the mid-60s and lasts until the end of life. Most people over 65 have retired from work, freeing up their time for hobbies, grandchildren, and other interests. Stamina, strength, reflex time, and the senses all decline during old age, and the number of brain cells decreases as well. The immune system becomes less efficient, increasing the risk of serious illnesses such as cancer and pneumonia. Diseases such as Alzheimer's disease that cause loss of mental function also become more common. and the situation: Two neighboring towns had different demographics. Hill town had younger inhabitants, most of them in their 30's and 40's. Lake town was inhabited by elderly people, most of them above 65 years of age. Answer the following question: Which town had more people with decreased stamina?
Ans: Lake

Given the background: The Hawaiian Islands ( Figure above ) are in the central Pacific Ocean. The islands are volcanoes that increase in age from southeast to northwest. The youngest island is the Big Island of Hawaii at the southeast end of the chain. The volcanoes get older through Maui, Kahoolawe, Lanai, Molokai, Oahu, Kauai, and Niihau Islands through the northwest. The Kilauea volcano on Hawaii has been erupting almost continuously since 1983. There are also eruptions at an underwater volcano called Loihi seamount. Loihi is the youngest volcano. Hawaii is a fantastic place to see volcanic eruptions and features. and the situation: Grant and Fox were talking about flying to Hawaii for a tour of the islands. Grant was born on the Big Island, while Fox never visited Hawaii. Answer the following question: Which friend lived farther from Niihau island?
Ans: Fox