Question

If elements with principal quantum number $n>4$ were not allowed in nature, the number of possible elements would have been :

• A. 40
• B. 60
• C. 44
• D. 108

Answer 1

Answer: (B)

Correct option: (A)

For a neutral atom, the atomic number of an element is equal to the number of electrons or protons present in an atom of the particular element.

Step 1: Determining the number of possible subshells
$n$ should not be greater than 4.

$Forn=1\to 1s$
$n=2\to 2s,2p$
$n=3\to 3s,3p,3d$
$n=4\to 4s,4p,4d,4f$

Step 2: Calculating the maximum number of element in nature
$n=1\Rightarrow 1s=2electrons$
$n=2\Rightarrow 2s,2p=2+6=8electrons$
$n=3\Rightarrow 3s,3p,3d=2+6+10=18electrons$
$n=4\Rightarrow 4s,4p,4d,4f=2+6+10+14=32electrons$

Total electrons $=2+8+18+32=60$
Thus, there can be a maximum of 60 elements that can exist in nature.