Question 1

Which element accounts for the greatest proportion of mass in the human body?

Accepted Answer

Oxygen

Question 2

A radioactive isotope of carbon, $$^{14}C$$, is used in dating ancient artifacts. What property makes $$^{14}C$$ radioactive?

Accepted Answer

It has an unstable combination of protons and neutrons in its nucleus.

Question 3

Which of the following best explains why iodine is considered an essential element for humans?

Accepted Answer

It is required for the synthesis of thyroid hormones.

Question 4

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

Accepted Answer

$$23 - 11 = 12$$ neutrons

Question 5

Which of the following statements about covalent bonds is correct?

Accepted Answer

Covalent bonds involve the sharing of pairs of valence electrons between atoms.

Question 6

Which of the following best describes the difference between a molecule of $$O_2$$ and a molecule of $$CO_2$$?

Accepted Answer

$$O_2$$ consists of two oxygen atoms bonded together, while $$CO_2$$ consists of one carbon atom double-bonded to two oxygen atoms.

Question 7

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

Accepted Answer

The molecule has a bent shape and oxygen is more electronegative than hydrogen, resulting in an uneven distribution of charge.

Question 8

Which type of chemical bond is responsible for the attraction between sodium and chloride ions in table salt ($$NaCl$$)?

Accepted Answer

Ionic bond

Question 9

A patient is injected with a radioactive isotope for a PET scan. Which property of the isotope allows it to be detected by the scanner?

Accepted Answer

It emits energy as it decays, which can be detected by the scanner.

Question 10

Which of the following statements about valence electrons is correct?

Accepted Answer

Atoms with a full valence shell are chemically unreactive.

Question 11

Which of the following best describes a hydrogen bond?

Accepted Answer

A weak attraction between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom.

Question 12

Which of the following is an example of a reversible chemical reaction in living systems?

Accepted Answer

$$CO_2 + H_2O$$ \rightleftharpoons H_2CO_3$$

Question 13

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

Accepted Answer

They have a full valence electron shell.

Question 14

Which of the following statements about van der Waals interactions is correct?

Accepted Answer

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

Question 15

A molecule has the formula $$C_6H_{12}O_6$. Which of the following statements is true?

Accepted Answer

It contains 6 carbon, 12 hydrogen, and 6 oxygen atoms.

Question 16

Which of the following best explains the importance of molecular shape in biology?

Accepted Answer

Molecular shape determines how molecules recognize and respond to one another.

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 describes electronegativity?

Accepted Answer

The ability of an atom to attract electrons toward itself in a chemical bond.

Question 19

Which of the following is a real-world example of the biological use of radioactive isotopes?

Accepted Answer

Using $$^{14}C to $$date fossils and ancient artifacts.

Question 20

Which of the following best explains why chemical reactions are often reversible in living systems?

Accepted Answer

The products of the reaction can react to form the original reactants.

The Chemical Context of Life: Study Notes for General Biology

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