Question 1

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

Accepted Answer

A compound has a fixed composition with elements combined in definite proportions, while a mixture has variable composition.

Question 2

Which of the following statements about metals is CORRECT?

Accepted Answer

Metals are malleable, ductile, and have high electrical conductivity.

Question 3

Which of the following is the correct electron configuration for a neutral atom of magnesium (Mg, atomic number 12)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$

Question 4

Which of the following elements is most likely to form a cation with a $$+1$$ charge?

Accepted Answer

Sodium (Na)

Question 5

A sample contains $$3.0$$ moles of $$CO_2. $$How many molecules of $$CO_2$$ are present in the sample? (Avogadro's number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$1.81 	imes 10$$^{24}$$

Question 6

Which of the following best explains why ionic compounds tend to have high melting points?

Accepted Answer

They consist of ions held together by strong electrostatic forces.

Question 7

Which of the following is the correct Lewis structure for methane ($$CH_4$$)?

Accepted Answer

A central C atom with four single bonds to four H atoms, each H having no lone pairs.

Question 8

Which of the following elements has the highest electronegativity?

Accepted Answer

Fluorine (F)

Question 9

Which of the following statements about isotopes is TRUE?

Accepted Answer

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

Question 10

Which of the following best describes the trend in atomic radius across a period from left to right in the periodic table?

Accepted Answer

Atomic radius decreases due to increasing nuclear charge.

Question 11

A student mixes $$NaCl ($$table salt) and $$H_2O ($$water) in a beaker. Which of the following best describes the result?

Accepted Answer

$$NaCl$$ dissolves in $$H_2O to $$form a homogeneous mixture (solution).

Question 12

Which of the following is the correct formula for the compound formed between magnesium and chlorine?

Accepted Answer

$$MgCl_2$$

Question 13

Which of the following best describes the Law of Definite Proportions?

Accepted Answer

A chemical compound always contains exactly the same proportion of elements by mass.

Question 14

Which of the following is a physical change?

Accepted Answer

Melting of ice

Question 15

Which of the following is the correct order of increasing ionization energy for the elements $$Na$$, $$Mg$$, and $$Al$$?

Accepted Answer

$$Na \u003c Mg \u003c Al$$

Question 16

A neutral atom of sulfur ($$S) $$has an atomic number of $$16$$ and a mass number of $$32. $$How many neutrons does it have?

Accepted Answer

$$16$$

Question 17

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

Accepted Answer

Ionic bonds involve the transfer of electrons from one atom to another, while covalent bonds involve the sharing of electrons.

Question 18

Which of the following is the correct set of quantum numbers for the last electron added to a phosphorus atom ($$Z=15$$)?

Accepted Answer

$$n=3,\ l=1,\ m_l=1,\ m_s=+\frac{1}{2}$$

Question 19

Which of the following best explains why chlorine ($$Cl_2) is a $$gas at room temperature while sodium chloride ($$NaCl) is a $$solid?

Accepted Answer

$$Cl_2$$ molecules are held together by weak intermolecular forces, while $$NaCl is $$held together by strong ionic bonds.

Question 20

Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

Accepted Answer

$$	ext{Average atomic mass} = (	ext{fraction}_1 	imes 	ext{mass}_1) + (	ext{fraction}_2 	imes 	ext{mass}_2)$$

Introduction to Chemistry: Foundations, Atomic Structure, and Chemical Bonding

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