Atoms and Molecules: Mass, Models and Applications

Section A: Core Ideas

Question 1mcq

Which statement correctly distinguishes molecular mass from formula unit mass?

A.Both terms mean mass of a single proton.

B.Molecular mass is used for molecules; formula unit mass is used for ionic compounds.

C.Molecular mass is used only for metals.

D.Formula unit mass is used only for gases.

Question 2mcq

Calculate the molecular mass of water,

H_2O

. Given

H=1

,

O=16

.

A.

18\,u

B.

17\,u

C.

34\,u

D.

16\,u

Question 3mcq

Calculate the formula unit mass of sodium chloride,

NaCl

. Given

Na=23

,

Cl=35.5

.

A.

46\,u

B.

35.5\,u

C.

23\,u

D.

58.5\,u

Question 4mcq

In an electron dot structure of chlorine, how many valence electrons are shown around one chlorine atom?

A.8

B.1

C.7

D.2

Question 5mcq

A ball-and-stick model of

CO_2

should show?

A.Two carbon atoms connected to one oxygen atom.

B.One carbon atom connected to two oxygen atoms.

C.A random mixture with no fixed ratio.

D.One carbon atom alone.

Section B: Application Practice

Question 6mcq

Which everyday substance is an ionic compound used as common salt?

A.

NaCl

B.

N_2

C.

H_2

D.

O_2

Question 7mcq

Why do we say formula unit mass of

NaCl

instead of molecular mass?

A.

NaCl

has no fixed ratio.

B.

NaCl

is an element.

C.

NaCl

contains no atoms.

D.

NaCl

is ionic and exists as a lattice, not as separate molecules.

Question 8mcq

Calculate the molecular mass of carbon dioxide,

CO_2

. Given

C=12

,

O=16

.

A.

28\,u

B.

32\,u

C.

44\,u

D.

40\,u

Question 9mcq

Calculate the formula unit mass of calcium oxide,

CaO

. Given

Ca=40

,

O=16

.

A.

64\,u

B.

56\,u

C.

24\,u

D.

40\,u

Question 10mcq

Which electron dot idea is correct for a hydrogen molecule,

H_2

?

A.Two hydrogen atoms share one pair of electrons.

B.Hydrogen forms an ionic lattice like

NaCl

.

C.No electrons are involved in bonding.

D.Each hydrogen loses seven electrons.