Question 1

Which four elements make up approximately 96% of the mass of living organisms?

Accepted Answer

Carbon, hydrogen, oxygen, and nitrogen

Question 2

An atom of phosphorus has an atomic number of 15 and an atomic mass of 31. How many neutrons does it have?

Accepted Answer

$$31 - 15 = 16$$ neutrons

Question 3

Which of the following best describes a trace element?

Accepted Answer

An element required by an organism in only minute quantities

Question 4

If an atom has 9 protons, 10 neutrons, and 9 electrons, what is its atomic number and mass number?

Accepted Answer

Atomic number: $$9$$, Mass number: $$19$$

Question 5

Which of the following statements about isotopes is correct?

Accepted Answer

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

Question 6

A PET scan uses a radioactive isotope of fluorine, fluorine-18. How many neutrons does fluorine-18 have?

Accepted Answer

$$18 - 9 = 9$$ neutrons

Question 7

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

Accepted Answer

They have a full valence shell of electrons

Question 8

An atom of oxygen has an atomic number of 8. How are its electrons distributed among the first, second, and third shells?

Accepted Answer

2 in the first shell, 6 in the second shell, 0 in the third shell

Question 9

Which of the following is true about the relationship between atomic number and the number of electrons in a neutral atom?

Accepted Answer

The atomic number equals the number of electrons in a neutral atom

Question 10

Which element is the most abundant in the human body by mass?

Accepted Answer

Oxygen

Question 11

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 particles and energy as it decays

Question 12

Which of the following best describes potential energy in the context of electrons in an atom?

Accepted Answer

Potential energy increases as electrons are farther from the nucleus

Question 13

If an atom gains an electron, what type of ion does it become?

Accepted Answer

An anion (negatively charged ion)

Question 14

Which of the following elements is considered a trace element in the human body?

Accepted Answer

Zinc

Question 15

Which of the following statements about matter is correct?

Accepted Answer

Matter is anything that takes up space and has mass

Question 16

A carbon atom has 6 protons, 6 neutrons, and 6 electrons. What is its atomic mass?

Accepted Answer

$$6 + 6 = 12$$

Question 17

Which of the following best explains why elements in the same group (column) of the periodic table have similar chemical properties?

Accepted Answer

They have the same number of valence electrons

Question 18

Which of the following is a correct statement about atomic mass and mass number?

Accepted Answer

Atomic mass is the weighted average of all isotopes, while mass number is the sum of protons and neutrons in a specific atom

Question 19

Which of the following elements is NOT one of the four most abundant elements in living organisms?

Accepted Answer

Sodium

Question 20

A scientist discovers a new organism whose body is composed of 70% oxygen, 15% carbon, 10% hydrogen, and 3% nitrogen. Which element is most likely to be classified as a trace element in this organism?

Accepted Answer

Zinc

The Chemical Context of Life: Atomic Structure and Elements

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