Question 1

Which of the following best describes an element?

Accepted Answer

A substance that cannot be broken down into other substances by chemical means.

Question 2

Which group of elements is most abundant in living organisms?

Accepted Answer

C, H, O, N, P, S

Question 3

A patient presents with a goiter due to iodine deficiency. Which of the following best explains the biological role of iodine?

Accepted Answer

Iodine is required for the synthesis of thyroid hormones.

Question 4

Which of the following statements about compounds is correct?

Accepted Answer

Compounds are substances composed of two or more elements in a fixed ratio.

Question 5

How many neutrons are present in a carbon-14 atom?

Accepted Answer

$$14 - 6 = 8$$

Question 6

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons.

Question 7

A radioactive isotope has a half-life of 5,730 years. If a sample originally contains 100 grams, how much remains after 11,460 years?

Accepted Answer

25 grams

Question 8

Which of the following best explains why water (H$$_2O) $$and hydrogen peroxide (H$$_2O$_2) $$have different properties?

Accepted Answer

They have different ratios of hydrogen to oxygen atoms.

Question 9

Which of the following is true about the atomic number of an element?

Accepted Answer

It is equal to the number of protons in the nucleus.

Question 10

Which of the following best describes a cation?

Accepted Answer

An atom that has lost electrons and is positively charged.

Question 11

Which of the following best explains why sodium (Na) and chlorine (Cl) form an ionic bond in table salt (NaCl)?

Accepted Answer

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

Question 12

Which of the following is a correct statement about hydrogen bonds?

Accepted Answer

They are weak bonds formed between a partially positive hydrogen and a partially negative atom (usually O or N).

Question 13

Which of the following best describes the difference between atomic mass and mass number?

Accepted Answer

Mass number is the sum of protons and neutrons, while atomic mass is the weighted average of all isotopes.

Question 14

Which of the following molecules is nonpolar due to its symmetry, despite having polar bonds?

Accepted Answer

CCl$$_4$$

Question 15

Which of the following best describes a chemical reaction?

Accepted Answer

A process that rearranges electrons to make and break chemical bonds.

Question 16

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

Accepted Answer

Using radioactive tracers to diagnose cancer with PET scans.

Question 17

Which of the following best explains why water is a polar molecule?

Accepted Answer

Oxygen is more electronegative than hydrogen, creating partial charges.

Question 18

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

Accepted Answer

$$17 + 18 = 35$$

Question 19

Which of the following best describes van der Waals interactions?

Accepted Answer

Weak attractions due to transient local partial charges in nonpolar molecules.

The Chemical Context of Life: Matter, Elements, and Atomic Structure

Study Guide - Practice Questions