Hazardous effects of shopping bags are studied in:

The study of the harmful effects of shopping bags, particularly plastic bags, on the environment falls under Environmental chemistry. This branch of chemistry deals with the chemical phenomena occurring in the environment, including pollution and its impact.

• Answer: $\boxed{\text{Environmental chemistry}}$

When tiny visible particles of a substance are dispersed through a medium and will eventually settle out, the mixture is called a suspension.

• Answer: $\boxed{\text{Suspension}}$

The maximum number of electrons that can be accommodated in a shell is given by the formula $2n^2$, where $n$ is the shell number. For the third shell, $n=3$.

$$2n^2 = 2(3)^2 = 2 \times 9 = 18$$

Therefore, the third shell can accommodate a maximum of 18 electrons.

• Answer: $\boxed{18}$

Oxygen has an atomic number of 8, meaning it has 8 protons and 8 electrons. For the number of protons, electrons, and neutrons to be equal, the number of neutrons must also be 8.
The mass number (A) is the sum of protons (Z) and neutrons (N): $A = Z + N$.
In this case, $A = 8 + 8 = 16$.
So, the isotope is $^{16}\text{O}$.

• Answer: $\boxed{^{16}\text{O}}$

Oxygen is capable of forming all three types of bonds:

• Covalent bonds: In molecules like $\text{H}_2\text{O}$ or $\text{O}_2$.
• Coordinate covalent bonds: In polyatomic ions like the hydronium ion ($\text{H}_3\text{O}^+$), where oxygen donates a lone pair to form a bond with $\text{H}^+$.
• Ionic bonds: In compounds with highly electropositive metals, such as sodium oxide ($\text{Na}_2\text{O}$), where oxygen forms the $\text{O}^{2-}$ ion.

• Answer: $\boxed{\text{Oxygen}}$

The boiling point of a compound is primarily determined by the strength of its intermolecular forces. Among the given options, $\text{H}_2\text{O}$, $\text{HF}$, and $\text{NH}_3$ all exhibit hydrogen bonding, which is a strong intermolecular force. $\text{H}_2\text{S}$ only has weaker dipole-dipole and London dispersion forces.
Among the hydrogen-bonded compounds, water ($\text{H}_2\text{O}$) has the highest boiling point (100 °C) because each water molecule can form an average of two hydrogen bonds as a donor and two as an acceptor, leading to a highly extensive network of hydrogen bonds.

• Answer: $\boxed{\text{H}_2\text{O}}$

Mixtures are commonly classified into three main types: solutions, colloids, and suspensions.

• Answer: $\boxed{3}$

The chemical symbol for the element sodium is $\text{Na}$.

• Answer: $\boxed{\text{Na}}$

The mass of a proton is approximately $1.672 \times 10^{-27}$ kg.
The mass of an electron is approximately $9.109 \times 10^{-31}$ kg.
To find how many times a proton is heavier than an electron, we calculate the ratio of their masses:

$$\frac{\text{Mass of proton}}{\text{Mass of electron}} = \frac{1.672 \times 10^{-27}\text{ kg}}{9.109 \times 10^{-31}\text{ kg}} \approx 1836$$

A proton is approximately 1836 times heavier than an electron.

• Answer: $\boxed{1836}$

The mass of an electron is approximately $9.109 \times 10^{-31}$ kg. The options $+1.6022 \times 10^{-19}$ C and $+1.6022 \times 10^{-17}$ C represent charge, not mass.

• Answer: $\boxed{9.109 \times 10^{-31}\text{ kg}}$