Question

Identify the symbol for the missing element in each period.

P

S

Ar

Answer 1

Step 1: Find the period number.

• The number of shells = period number.
• According to the question, all the elements represented belong to the same period.

Step 2: Finding the period number for one element

Phosphorus$\left(\mathrm{P}\right)$:

• Atomic number: $15$
• Electrons per shell = $2,8,5.$
• The number of shells $=3$
• So, the elements belong to the period $3$
• The elements belonging to Period $3$ are Phosphorus$\left(\mathrm{P}\right)$, Sulphur $\left(\mathrm{S}\right)$, Chlorine $\left(\mathrm{Cl}\right)$, and Argon $\left(\mathrm{Ar}\right)$.

Hence, the missing element is Chlorine.