Q: Refer to the radioactive decay graph provided. If a fossil originally contained 80 grams of a radioactive isotope, how much would remain after 3 half-lives?

$$80 \times (\frac{1}{2})^3$ = 20$$ grams

Q: A radioactive isotope has a half-life of 2 years. If you start with 32 grams, how much will remain after 6 years?

$$32 \times (\frac{1}{2}$$)^{6/2}$$ = 4$$ grams

Question 1

Which of the following best describes why atoms form chemical bonds?

Accepted Answer

To achieve a stable electron configuration, typically by completing their valence shells.

Question 2

Refer to the radioactive decay graph provided. If a fossil originally contained 80 grams of a radioactive isotope, how much would remain after 3 half-lives?

Accepted Answer

$$80 	imes (\frac{1}{2})^3$ = 20$$ grams

Question 3

Which statement about isotopes is correct?

Accepted Answer

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

Question 4

A sodium atom (Na) reacts with a chlorine atom (Cl) to form sodium chloride (NaCl). What type of bond is formed, and what happens to the electrons?

Accepted Answer

An ionic bond is formed; sodium donates an electron to chlorine.

Question 5

Which of the following elements is NOT one of the four main essential elements that make up 96% of living matter?

Accepted Answer

Phosphorus (P)

Question 6

How many neutrons are present in an isotope of carbon with an atomic mass of 14?

Accepted Answer

$$14 - 6 = 8$$ neutrons

Question 7

Which of the following best explains why water (H$$_2O) is a $$polar molecule?

Accepted Answer

Oxygen is more electronegative than hydrogen, causing unequal sharing of electrons.

Question 8

Which of the following statements about electron shells is correct?

Accepted Answer

The first shell can hold a maximum of 2 electrons, and subsequent shells can hold up to 8 electrons.

Question 9

Which type of chemical bond is the strongest in biological molecules?

Accepted Answer

Covalent bond

Question 10

A radioactive isotope has a half-life of 2 years. If you start with 32 grams, how much will remain after 6 years?

Accepted Answer

$$32 	imes (\frac{1}{2}$$)^{6/2}$$ = 4$$ grams

Question 11

Which of the following best describes a hydrogen bond?

Accepted Answer

An attraction between a hydrogen atom with a partial positive charge and an electronegative atom with a partial negative charge.

Question 12

Which of the following is a trace element essential for life?

Accepted Answer

Iron (Fe)

Question 13

Which orbital hybridization is associated with a tetrahedral molecular shape?

Accepted Answer

sp3

Question 14

Which of the following best describes chemical equilibrium in a biological system?

Accepted Answer

The rate of the forward reaction equals the rate of the reverse reaction, and concentrations of reactants and products remain constant.

Question 15

Which of the following is an example of a van der Waals interaction?

Accepted Answer

Temporary attractions between nonpolar molecules due to random electron movement.

Question 16

Which statement about electron orbitals is correct?

Accepted Answer

P orbitals are dumbbell-shaped and can hold up to 6 electrons in total per shell.

Question 17

Which of the following best explains why the properties of H$$_2O $$and H$$_2O$_2$$ are so different?

Accepted Answer

They have different ratios of hydrogen to oxygen, resulting in different chemical properties.

Question 18

Which of the following is true about the relationship between protons, neutrons, and electrons in a neutral atom?

Accepted Answer

The number of protons equals the number of electrons.

Question 19

Which of the following best describes the role of radioactive isotopes in biology?

Accepted Answer

They can be used to date fossils and trace molecules in metabolic pathways.

Question 20

Which of the following best explains why molecular shape is important in biology?

Accepted Answer

The 3D shape of a molecule determines its function, such as enzyme-substrate binding.

The Chemical Context of Life: Foundations for General Biology

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