A mole is a fundamental unit in chemistry that allows chemists to count particles (such as atoms, molecules, or ions) by relating macroscopic quantities to the microscopic scale. Let's go through each of the provided statements:
1. It is 12 units of a given substance.
- This statement is incorrect because a mole does not reference 12 units of any substance. A mole is a much larger quantity.
2. It contains [tex]$6.02 \times 10^{23}$[/tex] grams of sodium chloride.
- This statement is incorrect because a mole is defined by the number of particles, not the mass. Specifically, a mole of sodium chloride would weigh approximately 58.44 grams (its molar mass), but this weight varies for other substances.
3. It is the mass of 12 carbon atoms.
- This statement is incorrect too because a mole consists of [tex]$6.02 \times 10^{23}$[/tex] atoms of carbon-12, not just 12 carbon atoms. The mass of one mole of carbon-12 is exactly 12 grams, but it pertains to [tex]$6.02 \times 10^{23}$[/tex] atoms.
4. It contains [tex]$6.02 \times 10^{23}$[/tex] particles of a given substance.
- This statement is accurate. A mole is defined as containing exactly [tex]$6.02 \times 10^{23}$[/tex] particles (Avogadro's number) of any given substance. This aligns perfectly with the concept of a mole in chemistry.
Therefore, the correct answer is:
It contains [tex]$6.02 \times 10^{23}$[/tex] particles of a given substance.
Thus, the statement that best describes a mole is the fourth one.
