Question

the atomic number is the number of protons in the nucleus.

which element has 20 protons in its nucleus?

• sodium
• calcium
• potassium

Explanation:

Identify definition of atomic number

The image states: "The atomic number is the number of protons in the nucleus."

Locate element with atomic number 20

We look for the element card with the number 20 in the top-left corner:

• Sodium (Na) has atomic number 11.
• Magnesium (Mg) has atomic number 12.
• Potassium (K) has atomic number 19.
• Calcium (Ca) has atomic number 20.

Match element name to options

The element with atomic number 20 is Calcium.

Answer:

• Sodium
• Calcium (Correct answer)
• Potassium