Question 1

Which of the following best explains why carbon is the backbone of biological molecules?

Accepted Answer

Carbon can form up to four covalent bonds, allowing for complex and stable molecular structures.

Question 2

Which of the following is NOT considered matter according to the biological definition?

Accepted Answer

Light

Question 3

An atom of sodium (Na) has 11 protons and 11 electrons. What is its atomic number and why?

Accepted Answer

Atomic number is 11 because it is defined by the number of protons.

Question 4

Which of the following elements is NOT one of the four most abundant in biological molecules?

Accepted Answer

Sulfur (S)

Question 5

A molecule of water ($$\mathrm{H_2O}) is $$held together by which type of bond?

Accepted Answer

Covalent bonds

Question 6

Which statement about compounds is correct?

Accepted Answer

Compounds consist of two or more chemically bound elements in a fixed ratio.

Question 7

Why are hydrogen bonds important in biological molecules?

Accepted Answer

They provide weak but significant interactions that stabilize structures like DNA and proteins.

Question 8

Which of the following best describes a polar covalent bond?

Accepted Answer

Electrons are shared unequally, resulting in partial charges on atoms.

Question 9

Given the following chemical formula: $$\mathrm{NaCl}$$, what type of bond holds the sodium and chlorine atoms together?

Accepted Answer

Ionic bond

Question 10

Which property of atoms determines their chemical behavior?

Accepted Answer

Number of electrons in the valence shell

Question 11

Why are oxygen and nitrogen important for life, even though they are not the most abundant elements in the Earth's crust?

Accepted Answer

They are highly reactive and form stable bonds in biological molecules.

Question 12

Which of the following is a correct definition of a molecule?

Accepted Answer

A molecule consists of one or more elements chemically bound together.

Question 13

If an atom has a full valence shell, what is its chemical reactivity?

Accepted Answer

It is unreactive and stable, like noble gases.

Question 14

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

Accepted Answer

A compound consists of two or more elements chemically bound in a fixed ratio.

Question 15

Which of the following is a real-world example of a molecule formed by nonpolar covalent bonds?

Accepted Answer

$$\mathrm{O_2$} ($$oxygen gas)

Question 16

A student claims that all compounds are molecules, but not all molecules are compounds. Is this statement correct?

Accepted Answer

Yes, because molecules can be made of one element, while compounds must have two or more elements.

Question 17

Which of the following best explains why atoms with unpaired valence electrons are chemically reactive?

Accepted Answer

They seek to fill their valence shells by forming bonds with other atoms.

Question 18

Which type of chemical bond is responsible for the unique properties of water, such as its high boiling point and surface tension?

Accepted Answer

Hydrogen bonds

Question 19

A scientist discovers a new molecule composed of only carbon and hydrogen atoms. Which type of bond is most likely to be found between these atoms?

Accepted Answer

Nonpolar covalent bonds

Question 20

Which of the following equations correctly represents the formation of sodium chloride from its elements?

Accepted Answer

$$\mathrm{Na} + \mathrm{Cl} \rightarrow \mathrm{NaCl}$$

Chemical Composition of Cells: Atoms, Bonds, and Organic Molecules

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