Question

Identify the symbol for the missing element in each period.

Rb

Sr

Zr

Answer 1

• The atomic number of Rubidium $\left(\mathrm{Rb}\right)$ is $37$.
• Electrons per shell are $2,8,8,18,1.$
• The number of shells = Period number = 5.
• So, the elements belong to period 5.
• The elements belonging to Period 5 are Rubidium $\left(\mathrm{Rb}\right)$, Strontium$\left(\mathrm{Sr}\right)$, Yttrium $\left(\mathrm{Y}\right)$, Zirconium $\left(\mathrm{Zr}\right)$.

Hence, the missing element is Yttrium$\left(\mathrm{Y}\right)$.