Q: A radioactive isotope has a half-life of 2 years. If you start with 80 grams, how much will remain after 6 years?

$$80 \times (\frac{1}{2})^3$ = 10$$ grams

Q: A sample contains 120 grams of a radioactive isotope with a half-life of 3 hours. How much will remain after 9 hours?

$$120 \times (\frac{1}{2})^3$ = 15$$ grams

Question 1

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

Accepted Answer

Oxygen is more electronegative than hydrogen, causing electrons to be shared unequally and creating partial charges.

Question 2

A radioactive isotope has a half-life of 2 years. If you start with 80 grams, how much will remain after 6 years?

Accepted Answer

$$80 	imes (\frac{1}{2})^3$ = 10$$ grams

Question 3

Which of the following best describes the difference between a molecule and a compound?

Accepted Answer

A molecule consists of two or more atoms bonded together, while a compound consists of two or more different elements bonded together.

Question 4

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

Accepted Answer

$$14 - 6 = 8$$ neutrons

Question 5

Which of the following best explains why sodium (Na) and chlorine (Cl) form an ionic bond, as shown in the diagram?

Accepted Answer

Sodium donates an electron to chlorine, resulting in oppositely charged ions that attract each other.

Question 6

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

Accepted Answer

Iron (Fe)

Question 7

If an atom has 17 protons, 18 neutrons, and 17 electrons, what is its atomic number and mass number?

Accepted Answer

Atomic number = 17, Mass number = 35

Question 8

Which statement best describes the role of valence electrons in chemical bonding?

Accepted Answer

Valence electrons are involved in forming chemical bonds because they are located in the outermost shell.

Question 9

Which of the following best explains why noble gases are generally unreactive?

Accepted Answer

Their valence shells are full, making them stable and unlikely to form bonds.

Question 10

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

Accepted Answer

Hydrogen bonds

Question 11

A sample contains 120 grams of a radioactive isotope with a half-life of 3 hours. How much will remain after 9 hours?

Accepted Answer

$$120 	imes (\frac{1}{2})^3$ = 15$$ grams

Question 12

Which of the following best describes a van der Waals interaction?

Accepted Answer

A temporary attraction between molecules due to momentary uneven electron distribution.

Question 13

Which orbital configuration correctly represents a neutral carbon atom?

Accepted Answer

$$1s^2$$, $$2s^2$$, $$2p^2$$

Question 14

Which of the following best explains why changing the ratio of elements in a compound (e.g., H$$_2O vs. H$_2O$_2) $$drastically alters its properties?

Accepted Answer

The chemical and physical properties of a compound depend on the specific elements and their ratios.

Question 15

Which hybridization and molecular shape is most likely for methane (CH$$_4$$)?

Accepted Answer

sp$$^3$$ hybridization, tetrahedral shape

Question 16

Which of the following is a real-world application of radioactive isotopes in biology?

Accepted Answer

Radiometric dating of fossils

Question 17

Which statement best describes chemical equilibrium in a biological system?

Accepted Answer

The rate of the forward reaction equals the rate of the reverse reaction, so concentrations remain constant.

Question 18

Which of the following best explains why lone pairs of electrons can distort the shape of a molecule?

Accepted Answer

Lone pairs exert greater repulsive force than bonding pairs, altering bond angles.

Question 19

Which of the following is true about the energy changes when an electron moves from a lower to a higher energy shell?

Accepted Answer

The electron absorbs energy to move to a higher shell.

The Chemical Context of Life: Foundations for Biology

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