Question

In the modern periodic table, \(3^{rd}\) period ends with _____.

• A. Ar
• B. Kr
• C. Ne
• D. Xe

Hint:

Every period in the periodic table generally ends with a noble gas. The third period ends with Argon \((Ar)\).

Answer 1

The Correct Option is A

Concept:
In the modern periodic table, elements are arranged in horizontal rows called periods and vertical columns called groups. The third period contains elements with three electron shells. The elements in the third period are: \[ Na,\ Mg,\ Al,\ Si,\ P,\ S,\ Cl,\ Ar \] The last element of the third period is Argon \((Ar)\), which is a noble gas.

Step 1: Writing the elements of the third period.
The complete third period is: \[ \text{Na} \rightarrow \text{Mg} \rightarrow \text{Al} \rightarrow \text{Si} \rightarrow \text{P} \rightarrow \text{S} \rightarrow \text{Cl} \rightarrow \text{Ar} \] From this sequence, we observe that Argon is the last element. \[ \boxed{\text{Third period ends with Argon (Ar)}} \]

Step 2: Checking the incorrect options.

• Ne (Neon) ends the second period.
• Kr (Krypton) ends the fourth period.
• Xe (Xenon) ends the fifth period. Hence, the correct answer is: \[ \boxed{(1)\ Ar} \]