Question

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> An element X has a mass number 4 and atomic number 2. Write the valency of this element?

Answer 1

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Mass number = 4
Atomic number = 2
X is Helium. It has 0 valency and it will not react with any other atom because it has its outer shell filled.