Question 1

Which of the following statements best explains why sodium (Na) and chlorine (Cl) readily form an ionic bond to create sodium chloride (NaCl)?

Accepted Answer

Sodium has a tendency to lose one electron, becoming a cation, while chlorine tends to gain one electron, becoming an anion; the resulting opposite charges attract, forming an ionic bond.

Question 2

Which element is most abundant in the human body by mass, and what percentage does it represent?

Accepted Answer

Oxygen, 65.0%

Question 3

A radioactive isotope of carbon, $$^{14}C$$, is used in medical imaging. What property of $$^{14}C$$ makes it useful as a tracer in biological systems?

Accepted Answer

It decays spontaneously, emitting particles and energy that can be detected.

Question 4

Which of the following best describes the difference between a compound and an element?

Accepted Answer

An element is a substance that cannot be broken down by chemical reactions, while a compound consists of two or more elements in a fixed ratio.

Question 5

Which of the following is true regarding the atomic number and atomic mass of an element?

Accepted Answer

The atomic number is the number of protons in the nucleus, while the atomic mass is the sum of protons and neutrons.

Question 6

Which of the following best explains why water ($$H_2O) is a $$polar molecule?

Accepted Answer

The oxygen atom is more electronegative than hydrogen, causing unequal sharing of electrons and partial charges.

Question 7

Which type of chemical bond is responsible for the attraction between water molecules, allowing insects to walk on water?

Accepted Answer

Hydrogen bonds

Question 8

If an atom has 6 protons, 6 neutrons, and 6 electrons, what is its atomic number and mass number?

Accepted Answer

Atomic number: 6, Mass number: 12

Question 9

Which of the following elements is considered a trace element in the human body?

Accepted Answer

Iron

Question 10

Which statement best describes chemical equilibrium in a reversible reaction?

Accepted Answer

The forward and reverse reactions occur at the same rate, so the concentrations of reactants and products remain constant.

Question 11

Which of the following best explains why noble gases are chemically inert?

Accepted Answer

They have a full valence shell, so they do not tend to gain, lose, or share electrons.

Question 12

Which of the following is a correct representation of a double covalent bond?

Accepted Answer

$$O=O$$

Question 13

Which of the following best describes the role of valence electrons in chemical bonding?

Accepted Answer

Valence electrons are those in the outermost shell and determine the chemical behavior of an atom.

Question 14

Which of the following is an example of a chemical reaction that is highly favorable and releases energy?

Accepted Answer

$$2H_2 + O_2$ \rightarrow 2H_2O$$

Question 15

Which type of weak chemical interaction is responsible for the adhesion of gecko toe hairs to surfaces?

Accepted Answer

Van der Waals interactions

Question 16

Which of the following best describes the difference between polar and nonpolar covalent bonds?

Accepted Answer

Polar covalent bonds have unequal sharing of electrons due to differences in electronegativity, while nonpolar covalent bonds have equal sharing.

Question 17

Which of the following is true about isotopes of an element?

Accepted Answer

Isotopes have the same number of protons but different numbers of neutrons.

Question 18

Which of the following elements is most likely to form three covalent bonds in biological molecules?

Accepted Answer

Nitrogen

Question 19

Which of the following best explains why the shape of a molecule is important in biological systems?

Accepted Answer

Molecular shape determines how molecules recognize and respond to one another, affecting biological function.

The Chemical Context of Life: Foundations for General Biology

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