Question 1

Which of the following statements 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, 12 neutrons, and 11 electrons. What is its atomic number and mass number?

Accepted Answer

Atomic number: 11, Mass number: 23

Question 4

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

Accepted Answer

Phosphorus

Question 5

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

Accepted Answer

Covalent bond

Question 6

Which of the following best describes a compound?

Accepted Answer

A substance consisting of two or more chemically bonded elements in a fixed ratio

Question 7

Why are atoms with unpaired valence electrons chemically reactive?

Accepted Answer

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

Question 8

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

Accepted Answer

Hydrogen bonds are weak interactions that occur between a hydrogen atom and an electronegative atom like oxygen or nitrogen.

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 oxygen makes it essential for the formation of polar covalent bonds in biological molecules?

Accepted Answer

Its high electronegativity

Question 11

A molecule has the formula $$\mathrm{C_6H_{12}O_6$}. $$Which of the following statements is true?

Accepted Answer

It is a compound made of three different elements.

Question 12

Which of the following best explains why the distribution of elements in the Earth's crust differs from that in the human body?

Accepted Answer

Biological processes selectively use elements that form stable covalent bonds, such as C, H, O, and N.

Question 13

Which of the following is true about valence electrons?

Accepted Answer

Valence electrons determine the chemical reactivity of an atom.

Question 14

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

Accepted Answer

Hydrogen bonds between water molecules

Question 15

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

Accepted Answer

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

Question 16

If an atom has 6 protons, 6 neutrons, and 6 electrons, what element is it and what is its atomic number?

Accepted Answer

Carbon, atomic number 6

Question 17

Which of the following statements about functional groups in organic molecules is correct?

Accepted Answer

Functional groups confer specific chemical properties to organic molecules.

Question 18

Which of the following best describes the difference between polar and nonpolar covalent bonds?

Accepted Answer

Polar covalent bonds involve unequal sharing of electrons due to differences in electronegativity; nonpolar covalent bonds involve equal sharing.

Question 19

Which of the following is the correct formula for calculating the mass number of an atom?

Accepted Answer

$$	ext{Mass number} = 	ext{Number of protons} + 	ext{Number of neutrons}$$

Question 20

A student mixes sodium ($$\mathrm{Na}) $$and chlorine ($$\mathrm{Cl}) in $$water and observes the formation of table salt ($$\mathrm{NaCl}). $$Which process best explains the bond formation?

Accepted Answer

Sodium donates an electron to chlorine, forming an ionic bond.

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

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