Question

An ion X²⁺ contains 18 electrons and 20 neutrons. Name the element.
1. Potassium
2. Calcium
3. Magnesium
4. Argon
5. None of the Above/ More than one of Above

Answer 1

Correct Answer - Option 2 : Calcium

The Correct Answer is option 2 i.e. Calcium.

• Atomic number is defined as the number of protons or the number of electrons that are present in an electrically neutral atom.
• Atomic no. = No.of electrons - (negative charge) + (positive charge)
• Thus,
  • At. no.= 18+(+2) = 20
  • Mass no. = 20 + 20 = 40
• Atomic Mass no of Calcium is 20
• Mass number is defined as the sum of the number of protons and neutrons that are present in an atom.