Question

The number of elements present in period 4th of long form of periodic table are

• A. 2
• B. 8
• C. 18
• D. 32

Answer 1

The Correct Option is C

Step 1: Recall the structure of the periodic table.

The number of elements in a period depends on the subshells being filled:

• Period 1: \( 1s \) → 2 elements,
• Period 2: \( 2s, 2p \) → 8 elements,
• Period 3: \( 3s, 3p \) → 8 elements,
• Period 4: \( 4s, 3d, 4p \) → 18 elements.

 

Step 2: Identify the number of elements in the 4th period.

In the 4th period, the \( 4s \), \( 3d \), and \( 4p \) subshells are filled. These subshells accommodate a total of:

\[ 2 (\text{from } 4s) + 10 (\text{from } 3d) + 6 (\text{from } 4p) = 18 \, \text{elements}. \]

Final Answer: The number of elements in the 4th period is \( \mathbf{18} \), which corresponds to option \( \mathbf{(3)} \).