Question

What is the symbol for an atom containing 20 protons, 18 electrons and 22 neutrons?

• A. \(Mg^{2+}\)
• B. \(Sc^{3+}\)
• C. \(Ca^{2+}\)
• D. \(K^{+}\)

Hint:

Atomic number = Number of protons. Charge = Number of protons $-$ Number of electrons.

Answer 1

The Correct Option is C

Concept: The identity of an element is determined by its atomic number, which is equal to the number of protons present in the nucleus. The charge on an atom or ion depends upon the difference between the number of protons and electrons.

Step 1: Determine the atomic number. Given: \[ \text{Number of protons}=20 \] Atomic number: \[ Z=20 \] The element having atomic number 20 is calcium. \[ \boxed{\text{Element} = Ca} \]

Step 2: Determine the ionic charge. Number of electrons: \[ 18 \] Number of protons: \[ 20 \] Net charge: \[ 20-18=+2 \] Therefore the ion is \[ Ca^{2+} \]

Step 3: Verify the mass number. Number of neutrons: \[ 22 \] Mass number: \[ A=20+22=42 \] Thus the species is \[ ^{42}_{20}Ca^{2+} \] Among the options, this corresponds to \[ \boxed{Ca^{2+}} \] Hence the correct option is \[ \boxed{(3)} \]