Atomic Number & Mass Number Practice

What is the number of protons in a magnesium atom ?

• 12

• 24

• 23

• 8

Answer explanation

A magnesium atom has 12 protons, which is its atomic number. This number defines the element and distinguishes it from others. Therefore, the correct answer is 12.

Tags

NGSS.MS-PS1-1

What is the number of electrons in a chlorine atom?

• 35

• 11

• 18

• 17

Answer explanation

A chlorine atom has an atomic number of 17, which means it has 17 protons and, in a neutral atom, the same number of electrons. Therefore, the correct answer is 17.

Tags

NGSS.MS-PS1-1

How many Neutrons are present in a sodium atom ?

• 12

• 11

• 0

• 23

Answer explanation

A sodium atom has an atomic number of 11, which means it has 11 protons. The atomic mass is approximately 23. To find the number of neutrons, subtract the number of protons from the atomic mass: 23 - 11 = 12. Thus, the correct answer is 12.

Tags

NGSS.MS-PS1-1

What is the atomic number?

• the number of protons

• the number of protons and neutrons

• the number of neutrons

• the number of protons and electrons

Answer explanation

The atomic number is defined as the number of protons in an atom's nucleus. This is the key characteristic that determines the element's identity, making "the number of protons" the correct answer.

What is the mass number defined as?

• the number of protons

• the number of protons and neutrons

• the number of neutrons

• the number of protons and electrons

Answer explanation

The mass number is defined as the total number of protons and neutrons in an atom's nucleus. This is why the correct answer is 'the number of protons and neutrons', as it accounts for both types of nucleons.

Tags

NGSS.MS-PS1-5

What is the atomic number of this atom?

• 1

• 3

• 4

• 7

Answer explanation

The atomic number of an atom represents the number of protons in its nucleus. The correct answer is 3, which corresponds to lithium (Li), as it has 3 protons.

Tags

NGSS.MS-PS1-1

What is the mass number of this atom?

• 1

• 3

• 4

• 7

Answer explanation

The mass number of an atom is the sum of its protons and neutrons. In this case, the atom has 7 nucleons (protons + neutrons), making the correct mass number 7.

Tags

NGSS.MS-PS1-1

The fluorine atom has an atomic number of

• 19

• 9

Answer explanation

The atomic number of an element is the number of protons in its nucleus. For fluorine, this number is 9, which corresponds to its position on the periodic table.

Tags

NGSS.MS-PS1-1

What is the mass number and atomic number of nitrogen?

• Mass number = 7, atomic number = 14

• Mass number = 14, atomic number = 7

Answer explanation

Nitrogen has an atomic number of 7, which indicates it has 7 protons. Its most common isotope has a mass number of 14, which is the sum of protons and neutrons. Therefore, the correct choice is mass number = 14, atomic number = 7.

Tags

NGSS.MS-PS1-1

The mass of one proton is much, much greater than the mass of one...

• neutron

• electron

Answer explanation

The mass of one proton is much greater than the mass of one electron. Protons and neutrons are both nucleons with similar masses, while electrons are much lighter, making them negligible in comparison.