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Hydrogen is a chemical element that is the lightest and most common gas in the universe. It has no color or smell and combines with oxygen to make water (H2O).

Nitrogen is a colorless and odorless gas that makes up most of the Earth's atmosphere. It is a chemical element that is essential for all living things to grow, especially plants.

A polymer is a large molecule made of many smaller units that are connected in a long chain. These materials can be natural, like rubber or wood, or synthetic, like plastic and nylon.

A prime number is a whole number greater than 1 that cannot be made by multiplying other whole numbers. It can only be divided evenly by itself and the number 1.

A ratio is a way to compare two amounts of things. It shows how much of one thing there is compared to another thing, like 2 parts water to 1 part juice.

The perimeter is the total distance around the outside edge of a shape or an area. In math and science, it is found by adding the lengths of all the sides of an object.

The diameter is the length of a straight line that goes through the center of a circle or a round object, connecting two points on its edge. It is the measurement that tells you how wide a circle or sphere is at its widest point.

A radius is a straight line from the center of a circle to its outer edge. It is also used to describe the distance from a center point in any direction to mark an area.

The circumference is the distance around the outside edge of a circle or a round object. It is a measurement that tells you how long the boundary of a round shape is.

A perpendicular is a line that meets or crosses another line at a 90-degree angle. It is used in science and math to describe two lines that are perfectly square to each other.