Question

Atoms of two elements P and Q have 5 electrons in $2^{nd}$ shell and $3^{rd}$ shell respectively. What will be the atomic numbers of these elements?

• A. 4 : 15
• B. 5 : 15
• C. 7 : 13
• D. 7 : 15

Answer 1

Answer: (D)

7 : 15

P has $5$ electrons in the second shell ($n=2$) , thus the electronic configuration is: $2,5$ and atomic no. $=7$
Q has $5$ electrons in the third shell ($n=3$) , thus the electronic configuration is: $2,8,5$ and atomic no. $=15$.