Which of the following is NOT a description of compounds?
===
OPTIONS:
- They can exist in the form of atoms or molecules.
- They consist of atoms of two or more elements bonded together.
- They have properties that are different from their component elements.
- They can be broken down into elements by chemical means but not physical means.

They can exist in the form of atoms or molecules.

This in turn causes the average temperature on Earth to rise. Which of the following observations supports that theory?
===
OPTIONS:
- The summer of 1998 was one of the hottest summer seasons on record.
- Carbon dioxide gas from cars and industry is a product of burning that produces heat.
- Carbon dioxide in the upper atmosphere absorbs and re-emits heat radiated from Earth's surface.
- Radiation on Earth's surface is increasing because of a hole in the ozone layers.

Carbon dioxide in the upper atmosphere absorbs and re-emits heat radiated from Earth's surface.

Use The Periodic Table of the Elements and the information below to answer the question. Magnesium metal (Mg) is grayish-white in color and reacts actively with water. Fluorine (F2) is a greenish-yellow gas at room temperature and is a member of the halogen family. These two elements react to produce magnesium fluoride (MgF2), a chemical commonly used in making windows and lenses. How do the elements magnesium (Mg) and fluorine (F2) produce the compound magnesium fluoride (MgF2)?
===
OPTIONS:
- by nuclear connection
- by physically combining
- by magnetic connection
- by chemically combining
by chemically combining