Question

The electronic configurations of elements are as-
\(A = 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2\)
\(B = 1s^2 2s^2 2p^6 3s^2 3p^5\)
Which of the following is formula of ionic compound that could be formed between these two elements A and B?

• A. \(\text{A}_2\text{B}\)
• B. \(\text{AB}_2\)
• C. \(\text{AB}_5\)
• D. \(\text{A}_5\text{B}_2\)

Hint:

Element A has two valence electrons (calcium) and B has seven (chlorine).

Answer 1

The Correct Option is B

Step 1: Plan:
Use valence electrons directly.

Step 2: Steps:
The outer shell of A is $4s^2$, giving two electrons to donate. The outer shell of B is $3s^23p^5$, seven electrons, so it needs one. A gives two electrons and each B takes one, so we need two B for each A: $\text{AB}_2$.

Final Answer:
The formula of the ionic compound is $\text{AB}_2$, option (B). \[ \boxed{\text{AB}_2} \]