11. what elements is sand made of?\n12. what is added to gorilla glass to make it stronger than normal…

Brief Explanations:

11. Sand is mainly composed of silicon and oxygen, often in the form of silicon - dioxide.
12. Gorilla Glass has aluminum and potassium added to enhance its strength compared to normal glass.
13. Most rare - earth elements come from China, with significant deposits also in the United States, Australia, and India.
14. The fifteen rare - earth elements are chemically similar because they have similar electron configurations in their outer shells, leading to similar chemical reactivity.
15. Rare - earth magnets are usually made of neodymium, iron, and boron (NdFeB magnets) or samarium and cobalt (SmCo magnets).
16. Rare - earth elements are in short supply due to their complex extraction processes, environmental concerns associated with mining, and concentrated global distribution of deposits.
17. There is limited research on how sharks react to rare - earth metals, but they may be affected by changes in their environment if these metals are present.
18. Since the specific parts of the lemon shark experiment are not provided, a detailed answer cannot be given. However, in general, an experiment on lemon sharks may involve aspects like experimental setup, variables, control groups, and data collection methods.

Answer:

11. Silicon and oxygen (usually as silicon - dioxide).
12. Aluminum and potassium.
13. China, with significant deposits also in the United States, Australia, and India.
14. Similar electron configurations in outer shells.
15. Neodymium, iron, and boron (NdFeB magnets) or samarium and cobalt (SmCo magnets).
16. Complex extraction processes, environmental concerns, concentrated global distribution of deposits.
17. Limited research, may be affected by environmental changes if present.
18. Insufficient information provided.