Question

how many protons does $^{40}$ca contain?
periodictable.pdf
○ a. 40
○ b. 22
○ c. 18
○ d. 20

Explanation:

Step1: Recall atomic number rule

The number of protons in an atom equals its atomic number, which is unique to each element.

Step2: Find Ca's atomic number

From the periodic table, calcium (Ca) has an atomic number of 20.

Step3: Match to proton count

Since atomic number = proton count, $^{40}$Ca has 20 protons.

Answer:

d. 20