Which of the following determines an element's identity?

A. the number of electrons
Incorrect. The number of electrons does not determine an element's identity.

B. the number of neutrons
Incorrect. The number of neutrons does not determine an element's identity.

C. the number of protons
Correct! The number of protons determines an elements identity.

D. the atomic mass
Incorrect. The atomic mass does not determine an element's identity.

Use the information below to identify the element. Click here to access the periodic table.

Atomic Mass: 31
Number of Protons: 15
Number of Neutrons: 16
Number of Electrons: 15

A. Gallium
Incorrect. Gallium would have 31 protons.

B. Phosphorous
Correct!

C. Sulfur
Incorrect. Sulfur would have 16 protons.

D. Zinc
Incorrect. Zinc would have 30 protons.

How many valence electrons does oxygen have? Click here to access the periodic table.

A. eight
Incorrect. Oxygen has eight electrons total.

B. sixteen
Incorrect. The atomic number of oxygen is sixteen.

C. six
Correct! Oxygen has 8 electrons. 2 on the first energy level and 6 valence electrons.

D. two
Incorrect. Oxygen has 8 electrons total. 2 on the first energy level and 6 valence electrons.

What determines an element’s reactivity?

A. the number of protons
Incorrect. The number of protons determines an elements identity.

B. the atomic number
Incorrect. The atomic mass is the same as the number of protons.

C. the atomic mass
Incorrect. The atomic mass is the number of protons and neutrons in the nucleus of an atom.

D. the number of valence electrons
Correct! The number of valence electrons determines the reactivity of an element.

Which element pictured below is the least reactive?

A. Correct! Atoms with zero or eight valence electrons are the least reactive. Neon has 8 valence electrons.	C. Incorrect. Atoms with zero or eight valence electrons are the least reactive. Carbon has 4 valence electrons.
B. Incorrect. Atoms with zero or eight valence electrons are the least reactive. Hydrogen has 1 valence electron.	D. Incorrect. Atoms with zero or eight valence electrons are the least reactive. Sodium has 1 valence electron.