Question 1

Which of the following best explains why sodium (Na), a highly reactive metal, and chlorine (Cl), a poisonous gas, can combine to form table salt (NaCl), which is safe to eat?

Accepted Answer

The combination of Na and Cl results in a compound with emergent properties different from those of the individual elements.

Question 2

Which four elements make up approximately 96% of the human body’s mass?

Accepted Answer

Oxygen, Carbon, Hydrogen, Nitrogen

Question 3

A neutral atom of sodium has an atomic number of 11 and a mass number of 23. How many neutrons does it have?

Accepted Answer

$$23 - 11 = 12$$

Question 4

Which statement best describes the relationship between electron shells and the energy of electrons?

Accepted Answer

Electrons in shells farther from the nucleus have higher potential energy.

Question 5

What is the maximum number of electrons that can occupy a single orbital?

Accepted Answer

2

Question 6

Which of the following best describes a polar covalent bond?

Accepted Answer

A bond where electrons are shared unequally between two atoms due to differences in electronegativity.

Question 7

Why is water (H$$_2O) $$considered a polar molecule?

Accepted Answer

Oxygen is more electronegative than hydrogen, creating partial charges on the molecule.

Question 8

Which type of bond is primarily responsible for holding together the two strands of DNA?

Accepted Answer

Hydrogen bonds

Question 9

A gecko can climb smooth walls due to thousands of weak interactions between its toe hairs and the wall surface. What type of interaction is primarily responsible for this phenomenon?

Accepted Answer

Van der Waals interactions

Question 10

Which of the following best explains why noble gases like neon (Ne) are chemically inert?

Accepted Answer

They have full valence shells, making them stable and unreactive.

Question 11

If an atom has 7 electrons in its outermost shell, what is its likely behavior in a chemical reaction?

Accepted Answer

It will tend to gain one electron to complete its valence shell.

Question 12

Which of the following is a trace element required by vertebrates for normal thyroid function?

Accepted Answer

Iodine (I)

Question 13

What is the main reason that ionic compounds like NaCl dissociate easily in water?

Accepted Answer

Water molecules surround and stabilize the ions, overcoming the ionic bond.

Question 14

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons.

Question 15

Which of the following is true about the molecular shape of methane (CH$$_4$$)?

Accepted Answer

It is a tetrahedron with hydrogen atoms at the corners.

Question 16

Which of the following best explains why morphine and endorphins can both bind to the same receptors in the brain?

Accepted Answer

They have similar molecular shapes, allowing them to fit the same receptor.

Question 17

A radioactive isotope of carbon, $$^{14}C$$, is used in medical imaging. What makes $$^{14}C $$radioactive compared to $$^{12}C$$?

Accepted Answer

$$^{14}C $$has an unstable nucleus that decays, emitting particles and energy.

Question 18

Which of the following best describes the process of energy absorption by an electron in an atom?

Accepted Answer

The electron moves to a higher energy shell farther from the nucleus.

Question 19

Which of the following is an example of an emergent property?

Accepted Answer

Table salt (NaCl) is edible, even though its components (Na and Cl) are hazardous.

Question 20

Which of the following best describes the role of hydrogen bonds in biological molecules?

Accepted Answer

They help stabilize the three-dimensional structure of proteins and DNA.

The Chemical Context of Life: Atoms, Elements, and Chemical Bonds

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