C, electrons. Ion<span> of an </span>element has<span> the </span>same<span> nucleus, the </span>same number<span> of protons and neutrons, with a </span>different number<span> of electrons.</span>
<span>It is important to use the Système Internationale (SI) units to describe motion, and other scientific concepts, firstly because the units are the most widely used. Unit choice is largely arbitrary, however, because many scientific units are derived from the base SI units, for example, the Newton is kg m s-2. Thus, secondly, more complex units are based on the bedrock of the SI units.</span>
An element would be the type of substance that only contains one kind of matter.
