Answer: Option (c) is the correct answer.
Explanation:
An element is defined as a substance which can never be broken down into simpler substances.
For example, sodium is a metal and it contains only atoms of sodium.
A compound is defined as a substance that contains two or more different elements that are chemically combined together in a fixed ratio by mass.
For example, KCl is a compound in which atoms are present in 1:1 ratio.
A mixture is defined as a substance in which two or more number of different substances are mixed together. Particles of a mixture never combine chemically to each other.
A solution is also known as a homogeneous mixture because in it the solute particles are evenly distributed.
So, when a student passes a magnet over 10 g of a powder. Four grams of the powder stick to the magnet, while 6 g do not then this means that particles were not chemically combined together and they are also not evenly distributed into the solution.
Thus, we can conclude that mixture identifies the substance.