Student Questions & Expert Answers

The shiny brown element X is copper (Cu). When copper is heated in air, it reacts with oxygen and forms a black compound called copper(II) oxide (CuO). This is a chemical reaction in which copper combines with oxygen.

Chemical equation:     2Cu + O₂ → 2CuO

A nephron is the smallest working unit of the kidney. It acts like a tiny filter that cleans the blood. Each kidney has about 1 million nephrons.

What does a nephron do?

1. Filters waste and extra water from the blood.
2. Returns useful substances like water, glucose, and salts back to the blood.
3. Forms urine, which carries waste out of the body.

Locomotion is the movement of a living organism from one place to another. Animals move to find food, water, shelter, or to escape from danger. Different animals use different body parts for locomotion, such as legs, wings, or fins.
For example a dog uses its legs to walk or run from one place to another. This movement is called locomotion.

Agitation is needed to clean clothes because soap breaks down the dirt, but the dirt still sticks to the cloth. When the clothes are rubbed, beaten, or moved around, friction is created. This friction loosens the dirt from the cloth, allowing the water to wash it away and make the clothes clean. 
For example If a shirt has mud on it, simply soaking it in soapy water may not clean it completely. Scrubbing it with a brush or washing it in a machine helps loosen the mud, making the shirt clean.

Two magnetic field lines do not cross each other because a magnetic field can have only one direction at a point. If two field lines crossed, it would mean the magnetic field has two directions at the same place, which is impossible.

Example: A compass needle always points in one direction at a particular point. If field lines crossed, the compass would not know which direction to point.