Question 1

Which of the following best explains why sodium (Na) and chlorine (Cl) combine to form sodium chloride (NaCl) with properties very different from the original elements?

Accepted Answer

Na and Cl form an ionic compound, resulting in emergent properties distinct from the elements.

Question 2

A patient is diagnosed with goiter due to a deficiency of an essential trace element. Which element is most likely deficient, and what is its biological role?

Accepted Answer

Iodine (I); required for normal thyroid gland activity.

Question 3

Which process describes the use of sunflower plants to remove toxic heavy metals from contaminated soils?

Accepted Answer

Phytoremediation

Question 4

Given a sodium atom with atomic number 11 and mass number 23, how many neutrons does it have? Use the formula $$	ext{Number of neutrons} = 	ext{Mass number} - 	ext{Atomic number}.$$

Accepted Answer

$$23 - 11 = 12$$ neutrons

Question 5

Which statement best describes the difference between atomic number and mass number?

Accepted Answer

Atomic number is the number of protons; mass number is the sum of protons and neutrons.

Question 6

Carbon-14 is used in radiometric dating because it is a radioactive isotope. Which property makes it useful for this purpose?

Accepted Answer

It emits energy and particles as it decays, allowing measurement of age.

Question 7

Which of the following best explains why water has a high surface tension?

Accepted Answer

Hydrogen bonds between water molecules create strong cohesive forces at the surface.

Question 8

A gecko can walk on walls due to van der Waals interactions. Which statement best describes these interactions?

Accepted Answer

They are weak attractions that occur only when atoms and molecules are very close together.

Question 9

Which of the following is a real-life example of a chemical reaction important for life, and what are its reactants and products? Use the equation $$6\ \mathrm{CO}_2 + 6\ \mathrm{H}_2\mathrm{O} + 	ext{sunlight} ightarrow \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\ \mathrm{O}_2.$$

Accepted Answer

Photosynthesis; reactants: $$6\ \mathrm{CO}_2$$ and $$6\ \mathrm{H}_2\mathrm{O}$$; products: $$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$$ and $$6\ \mathrm{O}_2$$

Question 10

Which property of water allows it to moderate temperature in coastal regions, as seen in the temperature differences between cities near the ocean and those inland?

Accepted Answer

Water can absorb or release large amounts of heat with only a slight change in temperature.

Question 11

Why does ice float on liquid water, and why is this important for aquatic life?

Accepted Answer

Hydrogen bonds in ice are more ordered, making ice less dense than liquid water, allowing it to float and insulate the water below.

Question 12

Which of the following best describes the difference between a covalent bond and an ionic bond?

Accepted Answer

Covalent bonds involve sharing electrons; ionic bonds involve the transfer of electrons.

Question 13

A solution has a pH of 5. Which of the following statements is true about this solution?

Accepted Answer

It is acidic and has a high concentration of $$\mathrm{H}^+$$ ions.

Question 14

Which property of water is most directly responsible for the movement of water from roots to leaves in plants?

Accepted Answer

Cohesion and adhesion due to hydrogen bonding

Question 15

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

Accepted Answer

A buffer minimizes changes in $$\mathrm{H}^+ or$$ $$\mathrm{OH}^-$$ concentration by accepting or donating hydrogen ions.

Question 16

Which of the following substances is most likely to be hydrophobic?

Accepted Answer

Oil

Question 17

Which of the following is a correct statement about isotopes?

Accepted Answer

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

Question 18

Which of the following best explains why water is an excellent solvent for ionic and polar substances?

Accepted Answer

Water molecules are polar, allowing them to surround and dissolve ionic and polar molecules.

The Chemical Context of Life: Essential Chemistry for Biology

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