Question 1

Which of the following statements best explains why two atoms with the same atomic number but different mass numbers are considered isotopes?

Accepted Answer

They have the same number of protons but different numbers of neutrons.

Question 2

A sample of an unknown element contains atoms with 17 protons and 18 neutrons. What is the correct symbol for this isotope?

Accepted Answer

35/17Cl

Question 3

Which subatomic particle is responsible for the unique identity of an element?

Accepted Answer

Proton

Question 4

An atom of element X has a mass number of 23 and contains 11 protons. How many neutrons does it have?

Accepted Answer

12

Question 5

Which of the following best describes a nucleon?

Accepted Answer

A particle found in the nucleus, either a proton or a neutron

Question 6

A certain isotope of magnesium is represented as 25/12Mg. How many protons and neutrons does it contain?

Accepted Answer

12 protons and 13 neutrons

Question 7

If an atom has 8 protons, 8 neutrons, and 8 electrons, what is its mass number?

Accepted Answer

16

Question 8

Which of the following would result if a neutron in the nucleus of an atom were replaced by a proton?

Accepted Answer

The atomic number would increase by one, changing the element.

Question 9

A hospital uses a radioactive isotope of iodine, 131/53I, for medical imaging. How many neutrons are present in this isotope?

Accepted Answer

78

Question 10

Which of the following statements is correct regarding the relationship between atomic number and mass number?

Accepted Answer

The mass number is always greater than or equal to the atomic number.

Question 11

A scientist discovers a new isotope of element Y with atomic number 20 and mass number 42. Which of the following is true?

Accepted Answer

It has 22 neutrons.

Question 12

Which of the following best explains why the atomic number is used to order elements in the periodic table rather than the mass number?

Accepted Answer

The atomic number uniquely identifies the element, while the mass number can vary due to isotopes.

Question 13

A neutral atom of 14/7N is found in the atmosphere. Which of the following is true about this atom?

Accepted Answer

It has 7 protons, 7 neutrons, and 7 electrons.

Question 14

Which of the following would be the correct way to represent an isotope of carbon with 7 neutrons?

Accepted Answer

13/6C

Question 15

A patient receives a dose of 60/27Co for cancer treatment. How many nucleons are present in each atom of this isotope?

Accepted Answer

60

Atomic Number and Mass Number in Atoms

Study Guide - Practice Questions