Find the atomic number of the element whose electronic configuration is $2, 8, 5$.

Write the formula of the product formed when the element $A$ (atomic number $19$) combines with the element $B$ (atomic number $17$). Draw its electronic dot structure. What is the nature of the bond formed?

Which of the following is the outermost shell for elements of period $2$?

Which of the following is the outermost shell for elements of period $2$?

How many vertical columns are there in the modern periodic table and what are they called?

It was found that the law of octaves was applicable only up to: