Question 1

Which of the following statements best explains why ice floats on liquid water?

Accepted Answer

Ice is less dense than liquid water because hydrogen bonds keep water molecules farther apart in the solid state.

Question 2

A radioactive isotope has a half-life of 2 years. If you start with 100 grams, how much will remain after 6 years?

Accepted Answer

$$100 \div 2^3$ = 12.5$$ grams

Question 3

Which property of water allows a water strider to walk on the surface of a pond?

Accepted Answer

Cohesion due to hydrogen bonding

Question 4

Which of the following best describes the difference between a cation and an anion?

Accepted Answer

A cation has more protons than electrons, while an anion has more electrons than protons.

Question 5

Which of the following elements is NOT one of the four that make up 96.3% of human body weight?

Accepted Answer

Sodium (Na)

Question 6

What type of bond is formed when two atoms share electrons equally?

Accepted Answer

Nonpolar covalent bond

Question 7

Which of the following best describes a buffer’s function in biological systems?

Accepted Answer

It minimizes changes in pH by absorbing or releasing hydrogen ions.

Question 8

A solution has a hydrogen ion concentration of $$10^{-4}$$ mol/L. What is its pH?

Accepted Answer

$$pH = -\log_{10}(10$$^{-4}$$) = 4$$

Question 9

Which of the following scenarios best illustrates the concept of oxidation and reduction?

Accepted Answer

Sodium loses an electron to chlorine, forming Na+ and Cl– ions.

Question 10

Why does water have a high specific heat compared to other substances?

Accepted Answer

Because hydrogen bonds must absorb heat to break, stabilizing temperature changes.

Question 11

Which of the following best explains why salt (NaCl) dissolves easily in water?

Accepted Answer

Water molecules surround and separate Na+ and Cl– ions due to their polarity.

Question 12

Which of the following is a trace element essential for life but required only in small amounts?

Accepted Answer

Iron (Fe)

Question 13

Which of the following best describes the difference between an isotope and an ion?

Accepted Answer

Isotopes differ in neutron number; ions differ in electron number.

Question 14

Which of the following best explains why coastal cities tend to have milder climates than inland cities?

Accepted Answer

Water’s high specific heat moderates temperature changes.

Question 15

Which of the following is true about van der Waals interactions?

Accepted Answer

They are weak attractions that occur when molecules are close together due to temporary charge differences.

Question 16

A molecule of ammonia (NH$$_3) $$forms hydrogen bonds with water. Which atom in ammonia is most likely to form a hydrogen bond with water’s hydrogen?

Accepted Answer

Nitrogen, because it is more electronegative than hydrogen.

Question 17

Which of the following best describes the octet rule?

Accepted Answer

Atoms tend to gain, lose, or share electrons to achieve eight electrons in their outer shell.

Question 18

Which of the following is an example of a polar covalent bond?

Accepted Answer

The bond between oxygen and hydrogen in a water molecule.

Question 19

If a solution has a pH of 3, how many times greater is its hydrogen ion concentration compared to a solution with a pH of 6?

Accepted Answer

$$10^{6-3}$$ = $$10^3 = 1000$ times greater

Question 20

Which of the following best explains why water is considered the 'solvent of life'?

Accepted Answer

Water’s polarity allows it to dissolve many polar and ionic substances.

Chapter 2: The Chemical Context of Life – Atoms, Molecules, and Water

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