$$\text{Number of neutrons} = \text{Mass number} - \text{Atomic number}$$

Question 1

Which of the following statements best describes an element?

Accepted Answer

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

Question 2

Which of the following is a trace element essential for the thyroid gland, and what is its recommended daily intake?

Accepted Answer

Iodine (I), 0.15 mg/day

Question 3

A neutral atom of nitrogen has an atomic number of 7 and a mass number of 15. How many neutrons does it have?

Accepted Answer

$$15 - 7 = 8$$ neutrons

Question 4

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

Accepted Answer

It consists of two or more elements combined in a fixed ratio.

Question 5

Which of the following is the correct formula to calculate the number of neutrons in an atom?

Accepted Answer

$$	ext{Number of neutrons} = 	ext{Mass number} - 	ext{Atomic number}$$

Question 6

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons.

Question 7

Carbon-14 is used in radiometric dating. If its half-life is 5,730 years, what fraction of the original Carbon-14 remains after 11,460 years?

Accepted Answer

$$\frac{1}{4}$$

Question 8

Which of the following best describes a covalent bond?

Accepted Answer

A bond formed by the sharing of a pair of valence electrons between atoms.

Question 9

Which of the following statements about polar covalent bonds is correct?

Accepted Answer

One atom has a greater electronegativity and pulls the shared electrons closer.

Question 10

A sodium atom (Na) loses one electron to become Na$$^+. $$What is the resulting charge and what type of ion is formed?

Accepted Answer

Positive charge; cation

Question 11

Which of the following best explains why table salt (NaCl) forms a crystal lattice structure?

Accepted Answer

Ionic bonds between oppositely charged ions arrange in a repeating pattern.

Question 12

Which of the following is a real-life application of radioactive isotopes in medicine?

Accepted Answer

Using radioactive glucose in PET scans to detect cancerous cells.

Question 13

Which of the following best describes a hydrogen bond?

Accepted Answer

A weak bond formed when a partially positive hydrogen atom is attracted to a partially negative atom in another molecule.

Question 14

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

Accepted Answer

They are weak attractions that occur due to transient local partial charges.

Question 15

Which of the following best describes what happens during a chemical reaction?

Accepted Answer

Atoms are rearranged as chemical bonds are broken and formed.

Question 16

Given the following chemical equation: $$2H_2 + O_2$ \rightarrow 2H_2O$$, which of the following statements is true?

Accepted Answer

The number of each type of atom is conserved during the reaction.

Question 17

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

Accepted Answer

They have full valence electron shells, making them stable.

Question 18

Which of the following is the correct electron configuration for an oxygen atom (atomic number 8)?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^4$$

Question 19

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 20

A molecule of methane (CH$$_4) is $$considered nonpolar. Which of the following best explains why?

Accepted Answer

The molecule is symmetrical, so the charge distribution is even.

Atoms, Elements, and Chemical Bonds: Foundations for Biology

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