CSS - PMS - CCE - PCS - General Science
Atomic Structure - Mass Number
Which quantity should not be confused with relative atomic mass?
A. Melting point only
B. State of matter
C. Mass number of a specific nuclide
D. Chemical symbol
Correct Answer: C
Mass number is an integer for one nuclide, whereas relative atomic mass is a weighted average over naturally occurring isotopes.
CSS - PMS - CCE - PCS - General Science
Atomic Structure - Mass Number
Can two different elements have the same mass number?
A. No, mass number uniquely defines an element
B. Only at high temperature
C. Yes, such nuclides are called isobars
D. Only if both are hydrogen
Correct Answer: C
Different elements can have the same mass number but different atomic numbers; these are isobars.
CSS - PMS - CCE - PCS - General Science
Atomic Structure - Mass Number
If A = 23 and Z = 11, how many neutrons are present?
A. 11
B. 34
C. 23
D. 12
Correct Answer: D
Neutrons = A − Z = 23 − 11 = 12.
CSS - PMS - CCE - PCS - General Science
Atomic Structure - Mass Number
An isotope is written as carbon-14. What does 14 represent?
A. Number of electron shells
B. Atomic number
C. Valency
D. Mass number
Correct Answer: D
The number following an element name in isotope notation usually gives the mass number.
CSS - PMS - CCE - PCS - General Science
Atomic Structure - Mass Number
Which particles contribute approximately one atomic mass unit each to mass number?
A. Protons and neutrons
B. Electrons only
C. Electrons and photons
D. Photons and neutrinos
Correct Answer: A
Protons and neutrons are nucleons and each has a mass close to 1 u.
CSS - PMS - CCE - PCS - General Science
Atomic Structure - Mass Number
Do isotopes of the same element necessarily have the same mass number?
A. Only if ionized
B. No
C. Yes, always
D. Only in gases
Correct Answer: B
Isotopes have the same proton number but different neutron numbers, so their mass numbers differ.
CSS - PMS - CCE - PCS - General Science
Atomic Structure - Mass Number
How can the number of neutrons be found if mass number and atomic number are known?
A. Atomic number divided by mass number
B. Atomic number squared
C. Mass number minus atomic number
D. Mass number plus atomic number
Correct Answer: C
N = A − Z because A = protons + neutrons and Z = protons.
CSS - PMS - CCE - PCS - General Science
Atomic Structure - Mass Number
An atom has 6 protons and 8 neutrons. What is its mass number?
A. 6
B. 2
C. 14
D. 8
Correct Answer: C
Mass number = 6 + 8 = 14.
CSS - PMS - CCE - PCS - General Science
Atomic Structure - Mass Number
Which symbol is commonly used for mass number?
A. pH
B. Z
C. e
D. A
Correct Answer: D
Nuclear notation typically uses A for mass number and Z for atomic number.
CSS - PMS - CCE - PCS - General Science
Atomic Structure - Mass Number
What is the mass number of an atom?
A. Number of electron shells
B. Total number of protons and neutrons in its nucleus
C. Number of electrons only
D. Number of protons only
Correct Answer: B
Mass number A equals protons plus neutrons.