The magnitude of the charge on an electron is approximately: A) 1023 ext C B) 10⁻²¹ ext C C) 1019 ext C D) 10⁻¹⁹ ext C

The magnitude of the charge on a single electron is a fundamental physical constant, known as the elementary charge. Its value is approximately $1.602 \times 10^{-19}$ Coulombs (C).

We are looking for an approximation, specifically the correct order of magnitude.

• $10^{23} \text{ C}$ is incorrect.
• $10^{-21} \text{ C}$ is incorrect.
• $10^{19} \text{ C}$ is incorrect.
• $10^{-19} \text{ C}$ matches the correct order of magnitude.

The final answer is $\boxed{\text{D) } 10^{-19} \text{ C}}$.

Helium (He) has an atomic number of 2. In a neutral atom, the number of electrons is equal to the atomic number. Therefore, each helium atom has 2 electrons.

One mole of any substance contains Avogadro's number ($N_A$) of particles.

Since each helium atom has 2 electrons, the total number of electrons in 1 mol of helium is:

The charge of a single electron ($e$) is approximately $1.602 \times 10^{-19} \text{ C}$.
The total negative charge is the product of the total number of electrons and the charge of one electron:

• A) $4.8 \times 10^4 \text{ C}$
• B) $9.6 \times 10^4 \text{ C}$
• C) $1.9 \times 10^5 \text{ C}$
• D) $3.8 \times 10^5 \text{ C}$

The calculated value $1.929 \times 10^5 \text{ C}$ is closest to $1.9 \times 10^5 \text{ C}$.

The final answer is $\boxed{\text{C) } 1.9 \times 10^5 \text{ C}}$.

An electrical insulator is a material that resists the flow of electric current. This means that electrons within the material are not free to move easily from atom to atom.

• A) containing no electrons: All matter contains electrons. This statement is incorrect.
• B) through which electrons do not flow easily: This accurately describes an electrical insulator. The electrons are tightly bound to their atoms and require a large amount of energy to become mobile.
• C) cannot be a pure chemical element: Many pure chemical elements, such as sulfur or phosphorus, are excellent insulators. Diamond (a form of carbon) is also an insulator. This statement is incorrect.
• D) must be a crystal: Insulators can be amorphous (non-crystalline) solids, such as glass or rubber. This statement is incorrect.

The final answer is $\boxed{\text{B) through which electrons do not flow easily}}$.