Question

An ion $X^{2+}$ contains 18 electrons and 20 neutrons. Calculate the atomic number and mass no. of element X. Name the element X.

• A. Atomic number -18, Mass number - 40, Argon
• B. Atomic number - 22, Mass number - 48, Titanium
• C. Atomic number - 20, Mass number - 40, Calcium
• D. Atomic number - 40, Mass number - 20, Calcium

Answer 1

The correct option is C

Atomic number - 20, Mass number - 40, Calcium

Originally, the no. of electrons = 18+2 = 20

Thus, no. of protons = 20

Mass number = no. of protons + no. of neutrons.

Mass number = 20 + 20 = 40

The name of the element is Calcium